摘要:

AbstractThis paper concerns our first set of experimental data on alkyl chitosans in acidic medium allowing to compare the roles of the degree of alkylation and that of the length of the alkyl chains on their physicochemical properties in aqueous solution. The balance between electrostatic repulsion (related to the fraction of ‐NH3+) and the hydrophobic attraction is discussed on the CC12sample, a chitosan modified with a C12aliphatic chain. A phase diagram is established separating the conditions for gel‐like structure formation and phase separation. The roles of the net charge and that of the temperature on the formation of hydrophobic aggregates are exami

ISSN:1022-1360    

DOI:10.1002/masy.19971130113

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractLiquid crystalline ordering in planar polymer brushes is investigated theoretically by numerical calculations within a self‐consistent field approximation. The brushes are formed by macromolecules with mesogenic groups in main chain and immersed in a solvent. Existence of a microphase segregated brush(MSB)regime with a collapsed orientationally ordered intrinsic sublayer and a swollen external sublayer is shown. At small grafting density, the transition from a conventional brush state to the microphase segregated state is a jump‐wise first order phase transition for a finite chain length (N). The magnitudes of the jumps in the average characteristics of the brush tend to zero in the limitN→ ∞ since this transition occurs only in a vanishingly small part (∝N−1/2) of the brush. High compressibility ofMSBbrush is demonstrated. The origin of phase transition in planar brushes i

ISSN:1022-1360    

DOI:10.1002/masy.19971130114

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractWhen a homopolymer adsorbs from dilute solution onto a solid surface it first attaches and then maximises its number of contacts with the substrate by means of a spreading process. Evidence for this spreading process can be obtained from experiments on the adsorption kinetics. We report on a case where the adsorption kinetics depend on the rate at which the polymer was supplied to the surface (a protein adsorbing onto silica). Also, we discuss competitive adsorption experiments in which one kind of chain molecule attempts to displace another one from the surface. In these experiments, the desorption rate of the displaced species reflects the spreading rate of the displacer. When this rate is slower than the supply of displacer molecules, oversaturated layers result that spontaneously eject polymer. We have measured the rate of these displacement‐driven desorption processes in various cases and conclude that it depends strongly on the energy of the segment‐surface bond. A model involving the diffusion of defects over the surface may account for this find

ISSN:1022-1360    

DOI:10.1002/masy.19971130115

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA ground‐state approximation (GSA) is employed to model the structure of an adsorbed layer of homodisperse and polydisperse polymer. The model uses the basic assumption that the volume fraction at a distance z from the surface of a component with chain length N can be written as the product of the square of an eigenfunction g(z) and the N‐th power of an eigenvalue eϵ. This approximation implies the neglect of end effects (tails): only loops are considered. For a homodisperse polymer, the eigenvalue is defined through ϵN = In(1/ϕb), where ϕbis the bulk solution concentration. The eigenfuction can be written in terms of two parameters: a “proximal” length D which through the boundary condition may be related to the adsorption energy, and a “distal” length which is inversely proportional to √ε. For a polydisperse polymer, D is the same as for a homodisperse polymer, but ε has to be computed from an implicit equation which involves a summation over all chain lengths present. The contribution of each chain length N in a mixed adsorbed layer is obtained by weighting with eεN.This approximate analytical model gives results which are in good agreement with numerical self‐consistent‐field calculations. Examples are given to illustrate the applicability of the model to polydisperse systems. These include adsorption preference of long chains in polymer mixtures and the difference between adsorption and desorption isotherms in polydisperse systems. Simple expressions are obtained for the chain length characterising the transition between (long) adsorbed and (short) non‐adsorbed chains and for the wi

ISSN:1022-1360    

DOI:10.1002/masy.19971130116

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe following surface‐active monomers with methacrylic group at the end of hydrophobic tail: 12‐methacryloyloxydodecanoic acid (12‐MAODA) and 12‐(methacryloyloxydodecanoyl)‐glycerophosphatidylcholine 12‐MAODPC) were synthesized and investigated. Both monomers are forming monolayers at the liquid/gas interfaces with liquid‐expanded and liquid‐condensed states at low and high surface pressures, respectively. These monomers have been polymerized in the monolayers just by soft UV‐irradiation (254 nm). Dependences of polymerization rate vs. surface pressure for both monomers have maxima (3.33*10−4s−1for 12‐MAODPC and 4.89*10−4s−1for 12‐MAODA) at about 8–10 mN/m. The higher polymerization rate of 12‐MAODA polymerization as compared to 12‐MAODPC is due to the more dense packing of the acid molecules in monolayers as compared to the lipid. Areas per monomer unit in the obtained polymeric monolayers are much smaller than those for the monomer one. The collapse pressures increase after monomer polymerization that evidences the increase of the monolayer stability in cas

ISSN:1022-1360    

DOI:10.1002/masy.19971130117

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractLarge scale Monte Carlo investigations of the interface between A‐rich and B‐rich phases of symmetric binary (AB) polymer mixtures are presented, using the bond fluctuation model of flexible chains with NA=NB=N=32 effective monomers. The temperature range studied, 0.144

ISSN:1022-1360    

DOI:10.1002/masy.19971130118

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

Abstract“Crew‐cut” aggregates of polystyrene‐b‐poly(acrylic acid) block copolymers can be prepared by dissolving the copolymers in N,N‐dimethylformamide (DMF) and adding water to the solution to induce aggregation of the styrene segments of the copolymer chains. The aggregates are formed at near‐equilibrium conditions, and their structures are subsequently frozen by isolating them into aqueous solution by dialysis. Aggregates of a number of different morphologies have been prepared. The morphologies, identified by transmission electron microscopy, consist of spheres, rods, vesicles, lamellae, large compound vesicles, large compound micelles, etc. The formation of aggregates of different morphologies can be controlled by varying the copolymer composition, by changing the initial copolymer concentration in DMF, by adding ions (e.g. NaCl, CaCl2, HCl and NaOH, etc), or by adding ho

ISSN:1022-1360    

DOI:10.1002/masy.19971130119

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractPolystyrene‐block‐poly(2‐cinnamoylethyl methacrylate) (PS‐b‐PCEMA) and poly(acrylic acid)‐block‐poly(2‐cinnamoylethyl methacrylate) (PAA‐b‐PCEMA) were synthesized. These polymers formed micelles with PCEMA as the core in solvents poor for the PCEMA block but good for the other blocks. When the PS block was much longer than the PCEMA block, star micelles were prepared. The PCEMA cores of these micelles were then photo‐crosslinked to yield PS star polymers. Nanospheres of PCEMA were obtained by photolyzing crew‐cut micelles of PAA‐b‐PCEMA, in which the water‐soluble PAA block was much shorter than the water‐insoluble PCEMA block.PS‐b‐PCEMA self‐assembled at silica and their THF/cyclopentane micellar solution interfaces to form diblock monolayers called polymer brushes, in which the insoluble PCEMA block spread like a melt on the silica surface and the chains of the soluble PS block stretched into the solution phase like bristles of a brush. By tuning the relative composition, PCEMA in bulk formed cylindrical micro‐domains dispersed in the continuous PS matrix. Irradiation of the PS‐b‐PCEMA brushes enabled our preparation of crosslinked PS‐b‐PCEMA monolayers. Nanofibers were prepared by dissolving in THF the irradiated PS‐b‐PCEMA fil

ISSN:1022-1360    

DOI:10.1002/masy.19971130120

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

ISSN:1022-1360    

DOI:10.1002/masy.19971130102

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY