Trends in Colloid and Interface Science III

362 Pages·1989·8.531 MB·English

by  D. S. Dimitrov, P. Doinov (auth.), P. Bothorel, E. J. Dufourc (eds.)

Progress in Colloid & Polymer Science • Vol. 79
PROGRESS IN COLLOID & POLYMER SCIENCE
Editors" H.-G. Kilian (Ulm) and G. Lagaly (Kiel)
Volume 79 (1989)
Trends in Colloid and
Interface Science III
Guest Editors" .P Bothorel and E. J. Dufourc (Talence)
0
Steinkopff Verlag • Darmstadt
Springer-Verlag. New York
ISBN 3-7985-0831-3 (FRG)
ISBN 0-387-91364-5 (USA)
ISSN 0340-255 X
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ecaferP
In ,8891 the yearly meeting thoef European Col- Interfaces, D. Structure and Stability of Colloids,
loid and Interface Society was (ECIS) held in Arca- and, .E Theoretical Studies of Colloids.
chon, France, from the 19th to the 22rid of Septem-
ber. The first such meeting took place in Como, On beohfa lf ECIS, we would like to thank all the
Italy, in ,7891 and was attented by 031 participants participants for their contributions and for their ve-
coming from 71 European countries. The Arca- ry stimulating discussions, all along the meeting;
chon meeting welcomed 022 scientists from -la the memberosf the Scientific Committee: .L Bur-
most all European countries and from North Ame- lamacchi, .B Jonsson, H. Lekkerkerker, .E Sack-
rica. This increase in participants shows the good mann and Th. Tadros who helped usf or the prepa-
healths of our still young society. ration of the scientific program; our colleagues
from the Centre de Recherche (CNRS) Pascal Paul
About 04 oral communications and 031 poster
for their collaboration in the organization of the
presentations were given in Arcachon. Thper esent
8891 meeting, and all the generous meeting spon-
volume collects full papers taken from communi-
sors.
cations and posters. This volume is arbitrarily di-
vided into 5 sections:
A. Colloids of Biological Interest, .B Colloids of Pierre Bothorel
Industrial Interest, .C Wetting, Adsorption and Erick .J Dufourc
stnetnoC VII
stnetnoC
Preface ................................................................................................... V
A. Colloids of biological interest
Dimitrov DS, Doinov P: Dielectrophoresis, instability, and electrofusion in membrane systems ..................... 1
Duwe HP, Zeman K, Sackmann E: Bending undulations of lipid bilayerasn d the red blood cell membrane: A comparative
study ................................................................................................... 6
Faucon JF, M616ard ,P Mitov MD, Bivas I, Bothorel P: Thermal fluctuations of giant vesicles and elastic properties ofbilayer
lipid membranes. The role of the excess surface ............................................................ 11
Genot C, Guillet S, Metro B: Rheological properties of gelatin gels filled with phospholipids vesicles. Dynamic and uniaxial
compression measurements ............................................................................... 81
Ivanova T, Georgiev G, Panaiotov I, Ivanova M, Launois-Surpas MA, Proust JE, Puisieux F: Behavior of liposomes pre-
pared from lung surfactant analogues and spread at the air-water interface ..................................... 24
Laggner ,P Kriechbaum M, Hermetter A, Paltauf F, Hendrix J, Rapp G: Laser-induced temperature jump and time-resolved
x-ray powder diffraction on phospholipid phase transitions ................................................... 33
Laroche G, P6zolet M, Dufourcq J, Dufourc E J: Modifications of the structure and dynamics of dimyristoylphosphatidic
acid model membranes by calcium ions and poly-L-lysines ................................................... 38
Lo Nostro ,P Niccolai A, Gabrielli G: Lipid mixtures in monolayer and BLM ..................................... 34
Masson G: Characterization of small lipid vesicles prepared by microfluidization ................................. 49
Puggelli M, Gabrielli G, Domini C: Mixed monolayers of two polypeptides at the water/air interface ............... 52
Quiquampoix H, Chassin ,P Ratcliffe RG: Enzyme activity and cation exchange as tools for the study of the conformation of
proteins adsorbed on mineral surfaces ..................................................................... 95
Salcedo J, Delgado A, Gonz~lez-Caballero F: Electrokinetic and stability properties of cholesterol in aqueous NaC1 and
NaC1 + bile salt solutions ................................................................................ 64
Solans C, Infante N, W~irnheim T: Phase behavior of cationic lipoaminoacid surfactant systems .................... 70
Saint-Pierre-Chazalet M, Billoudet F, Pileni MP: Cytochrome c monolayer and mixed surfactant-cytochrome c monolayer 76
Terech P: Orientation of rods formed bayg gregated surfactants in organic media: the steroid-cyclohexane physical gel case 18
Xenakis A, Valis TP, Kolisis FN: Use of microemulsion systems as media for heterogeneous enzymic catalysis ....... 88
B. Colloids of industrial interest
Charmot D: Preparation of monodisperse, magnetizable, composite metal/polymer microspheres ................... 94
Kriechbaum M, Degovics G, Tritthart J, Laggner P: Fractal structure of Portland cement paste during age herdening
analyzed by small-angle x-ray scattering .................................................................... 101
Poirier JE, Bourrel M, Castillo ,P Chambu C, Kbala M: Asphalt emulsions: experimental study of the cationic surfactant
adsorption at the asphalt-water interface .................................................................... 601
Quemada D: An overview of recent results on rheology of concentrated colloidal dispersions ...................... 211
Tadros ThF: Correlation of viscoelastic properties of concentrated dispersions with their interparticle interaction ..... 021
Tourinho F, Franck R, Massart R, Perzynski R: Synthesis and magnetic properties of manganese and cobalt ferrite ferro-
fluids ................................................................................................... 821
C. Wetting, adsorption and interfaces
Bennis K, Martinet ,P Schuhmann D, Vanel P: Adsorption of cetyltrimethyl ammonium at the free surface and at the
mercury electrode ....................................................................................... 531
Bracke M, De Voeght F, Joos P: The kinetics of wetting: the dynamic contact angle ............................... 241
Djafer M, Lamy I, Terce M: Interaction of metallic cations with the hydrous goethite (g-FeOOH) surface ........... 051
Earnshaw JC, McLaughlin AC: The surface viscoelasticity of surfactant solutions and high frequency capillary waves. 551
Earnshaw JC, Robinson D J: Aggregation in interfacial colloidal systems ......................................... 261
Gurfein ,V Perrot F, Beysens D: Stability of silica colloids and wetting transitions ................................. 761
Ilmain F, Candau S J: Quasi-elastic light scattering study of poly(acrylic acid) networks swollen with water ........... 271
Meunier J, Binks BP: Measurement of the bending elasticity of a monolayer: ellipsometry and reflectivity ........... 871
SureshK A, Nittmann J, Rondelez F: Pattern growthd uringt hel iquid expanded-liquid condensed phase transition inL ang-
muir monolayers of myristic acid .......................................................................... 481
VIII stnetnoC
Varoqui R, Pefferkorn E: Experimental and theoretical aspects on cluster size distribution of latex particlfelso cculating in
presence of electrolytes and water soluble polymers ......................................................... 491
D. Structure and stability of colloids
Aveyard R, Binks ,PB Clark S, Fletcher PDI: Aggregation and adsorption behavior in nonionic surfactant/oil/water systems 202
Binks ,PB Meunier J, Langevin D: Characteristic sizes, film rigidity and interracial tensions in microemulsion systems 208
Cazianis CT, Xenakis A: Different spin probe positions related to structural changes of nonionic microemulsions .... 214
Chittofrati A, Lenti D, Sanguineti A, Visca M, Gambi CMC, Senatra D, Zhou Z: Perfluoropolyether microemulsions. 218
Gazeau D, Bellocq AM, Roux D, Zemb T: Experimental evidence for bicontinuous structures in 3L phases .......... 226
Kalus J, Hoffmann H, Lindner P: Small-angle neutron scattering experiments of micellar solutions under shear ...... 233
Lerebours B, Perly B, Pileni MP: Polymerization of cetyltrimethylammonium methacrylate directe micelles .......... 239
Malliaris A: Microviscosities in alkane/surfactant ionic micelles ................................................. 244
Messier A, Schorsch G, Rouviere J, Tenebre L: On certain solved and unsolved problems with water/PDMS/surfactant
systems ................................................................. : ............................... 249
Paillette M, Belhadj-Tahar N: Interracial charges manifestations: Kerr and dielectric relaxation studies in a microemulsion
system ................................................................................................. 257
Peyrelasse J, Boned C, Saidi "Z Percolation phenomenon in waterless microemulsions ............................ 263
Philipse AP, Vrij A: Non-aqueous silica dispersions. Charged particle interactions studied by scattering of light ....... 270
Ravey JC, Gherbi A, St6b6 MJ: Fluorinated and hydrogenated nonionics in aqueous mixed systems ................ 272
Rouch J, SafouaneA , Tartaglia ,P Chen SH: The critical region of water-in-oil microemulsions: new light scattering results 279
Smits C, Briels W J, Dhont JKG, Lekkerkerker HNW: Influence of the stabilizing coating on the rate of crystallization of
colloidal systems ........................................................................................ 287
Te~ak D, Popovi6 S, Heimer S, Strajnar F: Liquid crystallinity in metal ion - dodecylbenzenesulfonate systems: x-ray
diffraction characterization ................................................................................ 392
Thunig C, Hoffmann H, Platz G: Iridescent colours in surfactant solutions ....................................... 297
E. Theoretical studies of colloids
Filipovi6-VincekoNv,i 6 Skrti6 D: Interactions between surfactant ions of opposite charge .......................... 308
Nallet F, Roux D; Prost J: Dynamic light scattering study of membrane interactions in colloidals mectics ............ 313
Prochaska K, Szymanowski J: Interfacial activity of 1-(2'-hydroxy-5'-methylphenyl)-octane-l-one oxime and the interfacial
mechanism of copper extraction ........................................................................... 123
Prochaska K, Alejski K, Szymanowski J: Polynomial approximation of interfacial tension isotherms and its use fork inetic
data interpretation of metal extraction ...................................................................... 327
Regnaut C, Ravey JC: Analysis of the adhesive sphere fluid as a reference model for colloidal suspensions .......... 332
Schuhmann D: Some thermodynamic models of progressive' micellization, shape of the surface pressure curves, and pre-
dictions on the distribution of intermediate aggregates ....................................................... 338
~krti6 D, Filipovi6-VincNe:k ovi6 Crystallization of calciumo xalatien the presence of sodium dodecyl sulphate. Quantita-
tive assessment of the effect of the surfactant on crystal growth and aggregation ................................ 543
Author Index .............................................................................................. 353
Subje~ Index .............................................................................................. 354
Progress in Colloid & Polymer Science rgorP diolloC myloP icS 79:1-5 )9891(
.A Colloids of biological interest
Dielectrophoresis, instability, and electrofusion in membrane systems
D. .S Dimitrov and .P Doinov
Central Laboratory of Biophysics, Bulgarian Academy of Bulgaria Sofia, Sciences,
:tcartsbA An approach which si based on knowledge from the chemistry colloid of sur-
faces and thin presented. is films It si useful for understanding the mechanisms of mem-
approach, brane instability, and as well as fusion, for optimization of electrofusion. cell It
focuses on the use of fields electric external to induce membrane approach (by dielectro-
phoresis), instability (by electroporation), reversible and fusion. Experimental data for
processes these and discussed. are explanations theoretical possible The conclusions basic
are: )1 methods and results from thin-film dynamics combined with laws of membrane
motion and deformation induced by useful be can fields electric external for understand-
mechanisms ing of membrane electrofusion and fusion in general; )2 be can electrofusion
optimized by measuring cell polarizability by dielectrophoresis thea nd voltage critical of
electroporation reversible of membranes.
:sdro wyeK Dielectrophoresis, ,ytilibatsni_ electrofusion, i0rotoplasts, .semosopil_
noitcudortnI liquid/liquid interfaces and membranes. However,
several between essential differences interfaces single
In chemistry, the colloid phenomena of aggregation
and membranes should be taken into account:
and coalescence of particles, bubbles, solid and drops
are mainly investigated on the basis of principles of )1 The intermembrane interactions, which are the
physical chemistry of surfaces and thin films. It has driving forces of membranes adhesion and fusion,
been shown that the specific thermodynamic and may different be from those for elgnis While interfaces.
dynamic properties of the films, liquid thin formed be- the electrostatic and hydration forces depend mainly
tween determine largely the approaching the surfaces, on the type of the surface atnhde between film liquid
aggregation and particular, in coalescence, the kinetics them, the dvearn depend interaction also forces Waals
of approach of deformable bubbles and drops and sta- on the membrane material and thickness and can be
bility of thin-liquid films [1-3]. quite different from those for parti- in liquid surfaces,
The theoretical and experimental results for colloid cular with respect to the dependence functional on the
systems in most cases cannot be used directly to de- separation distance; 2) the membranes be can perme-
scribe the biological complex membrane systems. The able thfeo r solution between them, inter- while single
basic physicochemical approaches and results from face are not. The effect of membrane hydraulic per-
that work may prove useful if combined witkhn owl- increase strongly can meability the rate of approach; )3
edge of the specific physicochemical properties of the membrane liquid immobile, tangentially while are
membranes. It has been proposed that the kinetics of surfaces are mobile. Adding surfactants can decrease
membrane adhesion and fusion can follow the basic and mobility tangential almost stop the of inter- liquid
stages of aggregation and coalescence of bubbles and faces; )4 the membrane depends tension on membrane
drops [2-7]. This may be true at least because of the area changes while liquid surface tension does not.
very similar, in identical, equations some cases which However, when surfactants are adsorbed onto the
describes the approach of tangentially immobile interface the tension surface depends oanr ea change;
2 ssergorP in Colloid and Polymer ,ecneicS LoV 79 )9891(
)5 equilibrium deformations of membranes are de- ters of the external constraints and the systems have
scribed by membrane tension, shear elasticity, bend- been found empirically.
ing elasticity, and osmotic effects due to volume This paper discusses some of our recent work, and
changes, while those of liquid intearrfea ces character- tries tmoa ke use of knowledge from colloid chemistry
ized only by surface tension. In many cases only the to explain and optimize some processes of motion and
effect of membrane tension is important and then, fusion in membrane systems.
mathematically, this case is identical to the case of a
single interface; the surface tension should be replaced
The model
by the membrane tension; 6) cell membranes have
complex structure, characterized by lateral and trans- Motion of membranes leading to fusion can bes plit
membrainneh omogeneity, and geometry where ener- into four main stages: )1 continuous approacho f two
gy-consuming processes (active membrane motions, membranes; 2) destabilization of the membrane sys-
villi formation, etc.) are dominant, unlike the case of tem, which can result in rupture of the intervening
"non-living" interface. liquid film, bending of the membranes, rupture of the
Membrane fusion requires close approach and de- membranes or rupture of the film atnhde membranes;
stabilization [8]. In electrofusion [9], the membrane 3) membrane fusion itself, and 4) post-fusion pheno-
contact is achieved by dielectrophoresis atnhde desta- mena such as expansion of the liquid film betweetnh e
bilization is induced by DC pulses. The basic advan- membranes and membrane shapree laxation. It is rea-
tage of the physical methods, in particular, of the elec- lized that some of the stages may not exist or may
tric fields, over conventional ones, e.g., by using che- ocicnu r a different way. In addition, this consideration
micals, is the possibility for fast control of the entire seems to ignore molecular mechanisms. The pheno-
process. This is due mainly to the much higher speed menological approach has the basic advantage that the
of propagation of the electric field than that of the theoretical formulae are functions of macroscopic
diffusion of chemical substances. Dielectrophoresis is quantities (membrane tension, viscosity, etc.), which
motion of particles in non-homogeneous AC fields can be measurede xperimentally and it is valid for any
[10]. It arises because of the interaction of the exter- particular molecular mechanism.
nal electric field with the dipoles due to particle, The total time of the fusion-process is the sum theo f
polarization induced by the field. At close approach times for the separate stages. The duration of the
the induced dipoles interact with each other. Actually, membrane fusion itself 3), (stage which is due to rather
this mutual interaction attaches the particles to fast molecular rearrangements, is commonly very
each other and overcomes the repulsion forces. The short. The durations otfh e other three stages can be
electric-field-induced membrane destabilization is approximately described by the solution of the follow-
due to the transmembrane potential and surface ingn on-linear, partial differential equation [2]:
tangential stresses which tend to decrease the thick-
[H3(OPlar)ll2u] )1(
ness of the membrane and increase its area. When the OHlOt + 2Lp = V
electric forces overcome the elastic and viscous
resistance of the membrane material, the membrane p + ~p + FI (H) = BA2H/2 - TAH/2. (2)
can break, which results, in many cases, in pore forma-
tion. The destabilized membranes fuse at close In the case of axisymmetric approach V =. r- 1 + alar
approach. The membrane shape changes. The cell and A = v(alar), r being the radial coordinate. Here
protoplasm intermingles. The cells spherize to form H(r, t) is the local separation of the membranes,
the fmal product - the cell hybrid (in case of cell t - time, L- hydraulic permeability of the mem-
fusion). Similar processes may occur with othmeerm - branes,/a - liquid viscosity, p - dynamic pressure in
brane systems. the liquid between the membranes, T - membrane
Consequently, cell electrofusion, dielectrophoresis, tension, - B membrane bending elasticity modulus,/-/
membrane instability, in particular electroporation, - disjoining pressure, eP -equilibrium pressure in the
are strongly interrelated, at the least because of the liquid. These equations should be combined with
similar physiochemical mechanisms. The basic physi- appropriate boundary conditions. The mathematical
cal phenomena involved in these processes are known difficulties arise from the highlyn on-linear equation
in principal. However, due to the complexity of the bi- .)1( We will use several simple solutions ftohre case of
ological systems, in most cases the optimum parame- spherical membranes, modeling, e.g., cells and lipo-
Dirnitrov and Doinov, Cell dielectrophoresis and electrofusion 3
somes. We will focus on cases where the driving force where the electric fields are applied in a four-electrode
for membrane approach is due to external electric chamber [13]. By measuring the cell velocity v as a
fields as is in dielectrophoresis. function of the applied voltage and the separation dis-
tance one can obtain the values of the coefficients a and
siserohportceleiD Ke. A typical value for pea protoplasts (radius 51 tim,
in 0.5 M mannitol solution, medium viscosity- 1.41.
By solving Eq. )1( for the case of very small separa- mPa s, • conductivity - 0.47 mS/m, temperature -
tions between the membranes [2] it was shown that 20 °C, frequency- 1 MHz) is Ke = .011 Polarizabilities
the rate of approach v = - dh/dt (h = H(r = 0)) fol- for protoplasts and other cells at different conditions
lows the Reynolds formula are summarized and presented in [14]. One thoef bas-
ic conclusions is that in the radio frequency range most
V = VRe = 2Fh3/3n~R . 4 )3( of the living cells behave as highly conductive spheres
and the dielectrophoretic force cF (Eq. (6)) can be esti-
R is the radius of membrane contact and F - driving mated by assuming the net cell polarizability eK of the
force. When the separation is large, the Taylor formula order of the relative permitivity of the surrounding
can be used medium (for water solutions of the order of I0 to .)001
This rule is also valid for determination of the interac-
V = VTa = Fh[6 rcttR 2 , )4( tion force i F [15]. In this case, however, the force be-
tween two conducting spheres is given by a complicat-
~P being the cell radius. An interpolation formula ]21[ ed expression, which can be evaluated only numeri-
describes the rate of approach at arbitrary separations cally [15]. Rather simple approximate formula can be
written in the form
(5)
V = i P = Vst VTa VRe/(Vst + ETa ) (VTa + VRe )
Fi = pF 1( + Ah-1), (8)
where the Stokes rate is Vst = F/6 rqaP~.
The driving force due to dielectrophoresis is com- where the constant A is of the order of 01 mzI for pea
monly given by ]01[ protoplasts of 51 mt.I radius [15].
The expressions for the driving dielectrophoretic
F = pF = 2 EV~Ko¢~R~ 2 = - aVE2~2 (6) force also allow us to estimate the radius of membrane
contact R by using a formula derived by solving Eq. )1(
where 0e is the permitivity of the free space Ke - effec- [2]
tive net polarizability of the cell, E - electric field in-
tensity, and a - polarizability coefficient [12]. At close 2 R = FP~/2 rtT, (9)
approach the dielectrophoretic force strongly increase
due to the interaction between the induced dipoles. which is a modification of the well-known Deryaguin-
Then one must use more general formula Kussakov expression for the equilibrium radius of
bubble to solid surface contact. For typical values of
F=Fp i + F (7) the electric field intensity (E = l0 s V/m and VE = 901
V/m [14]) and T = 1.0 mN/m Eq. )9( gives contact
where Fi is the additional force due to induced electric radii of the order of I tim for protoplasts (radii of the
interactions. The combination of Eqs. )5( and (7) order of 01 ~m) which is the value observed experi-
allows the calculation of the rate of approach for arbi- mentally [16]. Liposomes which have internal con-
trary separations and, respectively, the time of ductivity lower than that oft he external medium do
approach until the establishment of the membrane not show positive dielectrophoresis and are not
contact. In order to do that we need the experimental attracted to protoplasts by mutual dielectrophoresis
values of the polarizability coefficients (a) and the in- [17]. Therefore, in this case dielectrophoresis is not an
teraction force effective method to collect cells and liposomes for the
F i.
We constructed an assay for single cell dielectro- purposes of electrofusion.
phoresis, where a cylindrically symmetrical field is The basic conclusion from our experimental results
created between two concentric electrodes [12]. on dielectrophoresis and this consideration is that
Recentlyw e developed a more sophisticated method there arfer equencies (commonly in the ratio frequen-
4 ssergorP in Colloid and Polymer ,ecneicS LoV 79 (1989)
cy range) and medium conductivities for each type of The results for membrane breakdowfnr om the previ-
cell where the polarizability coefficients are maximal. ous section can be used tom ake the following conclu-
The electrofusion should be carried out at those condi- sions about how to get better fusion: )1 the applied vol-
tions in order to ensure minimal times of approach and tage should be of the order of or higher than the critical
maximal area of contact. voltage of reversible breakdown; 2) the pulse duration
should be rather short, and 3) in some cases making
the medium slightly hypotonic can facilitate the
Electrically induced membrane instability
fusion. However, larger membrane tensions, i.e., lar-
We developed theoretical models for electrical ger osmotic forces, can decrease the contact area (see
breakdown of membranes [6, 7, ,81 ]91 which are in Eq. (9)) and hinder the fusion.
agreement, at least qualitatively, with available experi- Recently, by electrofusion we produced hybrido-
mental data [20-22]. The calculation of the critical mas which secreted monoclonal antibodies against the
thickness of rupture ]6[ of the film between two Hc antigene of salmonella [24]. We also succeeded to
approaching membranes showed [23] that the dielec- fuse whole fragile yeast mutants with protoplasts of
trophoretic force is small to induce instability. There- non-fragile yeasts [25]. In all these experiments the
fore, we can expect that the membranes andt he film time of dielectrophoresis was ketpot a minimum, e.g.,
between them are destabilized during the high voltage not longer than 2 min, which corresponds ttoht eh eo-
DC pulse. Two basic conclusions of importance for retical estimations by the formula for the rate of
electrofusion are: mutual approach of cells (Eq. (5)). The fusing voltage
)1 Formation of pores depends on the applied vol- was higher than that for breakdown. The highest
tage and duration of exposure to the field. Higher vol- yields were obtained when the number of pulses was 2
tages should be applied for shorter times to induce or 3; this could be due to viscous effects in the film and
reversible breakdown anfdo rmation of pores. Apply- membrane shape relaxations, which take time.
ing the field for longer periods of time leads to irrever- For getting high yields with the electrofusion tech-
sible breakdown and in many cases to cell death. The nique it is especially important to have the right arran-
heat generation is proportional to the square of the gements of the electrodes and the appropriate cham-
applied voltage and the time of exposure. However, ber to place them in. For biotechnologpiucraplo ses,
the time of breakdown is inversely proportional to the i.e., for production of viable hybrids on a larger scale,
difference of the square of the applied voltage and its the helical chamber is good [26]. We constructed sev-
valcurei.t ical Therefore, when the applied voltages are eral types of chambers which can also be used for fun-
near to the critical value, the heat generation will be damental research, not only of biomembrane systems,
large because the pulse duratmiuosnt be long. Increas- but also of colloid systems - and in some cases for the
intgh e voltage to get breakdown leads to decrease of purposes of practice:
the heat generation. )1 The cylindrical chamber [12] was used for dielec-
2) The breakdown voltage depends on the mem- trophoretic measurements. The basic advantage of this
brane tension, respectively on the osmolarity of the chamber for fusion experiments is that the distribution
medium. Decreasing the solution osmolarity leads to of the electric field is known. A number of studies were
decrease of the breakdown voltage. Our experimental performed with this chamber [27-31]; 2) sputtered
results [21] showed that decreasing the tonicity of the metal on glass surfaces which form very thin elec-
medium leads to a very sharp decrease of the break- trodes; electrodes of different shapes were tested. The
down voltage in the regnieoanr to the isotonic condi- basic hope for these chambers is that they can ensure
tions. The further decrease of the tonicity does not very specific cell fusion; the yield is not high and it is
change the breakdown voltage, much further. difficuk to clean the electrodes without damaging
them. 3) Plane-parallel chambers: in this case the two
electrodes are flat and parallel to each other. The basic
Hectrofusion
advantage of this chamber is that the field is homoge-
It was foundt hat the functiondaelp endence of the neous atnhde cells approach each other by mutual die-
fusing voltage on the pulse duration for pea protoplasts lectrophoresis, i.e., the damaging field is effectively
correlates strongly to that for their electrical break- decreased; 4) the four-electrode chamber is [13] multi-
down [22]. This helps in choosing the most appropri- functiiotn al: can serve for electrofusion and electropo-
ate parameters of the electrical field for effective fusion. ration in homogeneous and non-homogeneous fields,