摘要:

AbstractWe synthesized a number of poly(dimethylsiloxane) (PDMS) polymers with different molecular weights, and prepared model PDMS networks with a systematic change of cross‐link density, and therefore elastic constant (K). Self‐adhesion studies of PDMS hemispheres using the JKR method—the contact mechanics of solids spreading their interfacial area under load—reveal that hysteresis which results from relaxation processes in the elastomer can be practically eliminated using stepwise loading and unloading protocols. The adhesion of crosslinked PDMS surfaces to self‐assembled monolayers with different chemical functionality was investigated. Interfacial H‐bonding was shown to be an important chemical interaction causing significant adhesion hysteresis. The number of H‐bonds between PDMS and silanol groups on SiO2/Si surfaces increased with time of the contact under a constant load, indicating pressure‐induced reorganization of the PDMS network near the interface. The interaction between PDMS and carboxylic acid groups showed somewhat smaller hysteresis which suggests weaker H‐bonding strength. The interaction between PDMS and functionalized biphenyl groups exhibited small hysteresis which is believed to be caused by dipolar interaction, whereas that between PDMS and nonpolar perfluorocarbon groups showed negligible hysteresis. The distinction in the behavior of the unloading data between H‐bonding related interaction and dipolar interaction seems to indicate the difference in the nature between non‐specific (van der Waals, dipolar) and specific (donor‐acceptor, H‐bond

ISSN:1022-1360    

DOI:10.1002/masy.19981260103

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe adsorption and self‐organisation process of alkyl‐phosphonic acids and phosphoric acid monoalkyl esters on technical aluminium surfaces have been investigated by different surface sensible techniques: Grazing angle FT‐IR‐ spectroscopy, angle dependent XPS and Auger‐ spectroscopy. The aim of these studies was to replace the present technical procedure for pretreatment of aluminum surfaces with Chromate acid in order to improve the corrosion inhibition and the coating adhesion.The ability for self‐assembly is given by substances which have a surface reactive group and a long‐aliphatic or aromatic spacer and a supramolecular order is built‐up between these spacers. The results show that these molecules are able to adsorb spontaneously onto the aluminum surface and subsequently a structured molecular order is formed.These effects were confirmed by industrial linked adhesion and

ISSN:1022-1360    

DOI:10.1002/masy.19981260104

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractProton‐conducting polymer membranes are utilized as the solid electrolyte in low temperature polymer electrolyte fuel cells (PEFC), which are efficient energy converters. We have selected the process of radiation grafting and subsequent sulfonation to prepare novel membranes because of its feasibility as a low cost production method. Investigations of the two first preparations steps, i.e., irradiation and grafting, lead to insight concerning the optimization of these two steps and the dependence of the final membrane properties on the various preparation parameter

ISSN:1022-1360    

DOI:10.1002/masy.19981260105

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe adsorption of ions and amphiphilic molecules on solid polymers is investigated by direct force measurements using an atomic force microscope (AFM). It is shown that electrolyte ions are changing the surface potentials of the solid polymers as well as their adhesive properties. The experiments show that the interaction with a negatively charged probe is dramatically decreased by the adsorption of anions. The adsorption isotherms are determined by zeta potential measurements (streaming potential of flat plates). In presence of adsorbing anions, the attractive interaction and the adhesion are reduced and can be eliminated completely.So, even solutions of simple electrolyte ions can be applied intentionally in order to modify the interaction of polymer surfaces. A wide variety of technological applications becomes accessible.

ISSN:1022-1360    

DOI:10.1002/masy.19981260106

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractDe Gennes predicted the self‐similar structure φ(z) ∞z−αfor adsorbed polymer layers in the semi‐dilute (central) region of the adsorption profile of homopolymers. This power‐law behaviour is recovered in mean‐field SCF calculations. In this case the exponent is α = 2 in good solvents provided D «z «d, where D is the proximal length and d the distal length. We use a ground‐state approximation (GSA) to derive expressions for the two lengths D and d, and show that in the central region the profile is in good approximation given by φ = 1/3(z + D)−2exp(‐(z + D)2/3d2). Unless the chains are extremely long the condition D«z«d is difficult to obtain and corrections on the exponent are necessary. For most chain lengths in the experimental range, the central region is quite narrow. It is shown that for high adsorption energies (small D) α = 2 + 2d−1in leading order, where d = R/, with R the radius of gyration and φbthe bulk solution concentration. For weak adsorption the proximal length D is larger, which leads to a smaller exponent α. The d−1correction is in excellent agreement with numerical self‐consistent‐field calculations. In poor solvents we have φ = 1/2(z + D)−1exp(‐2(z + D)2/3d2) and α = 1 + 4d−1in the strong adsorption limit, which implies a larger correction in this case. Our analysis suggests that in a polymer adsorption profile with excluded‐volume correlations (where α = 4/3) non‐universal aspects wo

ISSN:1022-1360    

DOI:10.1002/masy.19981260107

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractSlightly cross‐linked polyelectrolytes absorb oppositely charged surfactants in aqueous media. Transfer of amphiphilic ions from solution into the swollen network proceeds as a frontal heterogeneous cooperative reaction causing a collapse of the original polyelectrolyte gel. Small and wide angle X‐ray diffraction data show that electrostatic complex formed as a result of the reaction consists of lamellar type surfactant micelles embedded in a polyelectrolyte network. It is also shown that such complexes contain equimolar amount of surfactant ions and ionized polyelectrolyte units paired with amphiphil head groups. In other words a charged network is not able to bind surplus oppositely charged surfactant ions. However, it is still able to solubilize a substantial amount of a nonionized surfactant. Chemical structure of surfactants strongly affect internal structure of lamellae and stability of the comple

ISSN:1022-1360    

DOI:10.1002/masy.19981260108

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe combination of two oppositely charged polyelectrolytes results in polyelectrolyte complexes. The simultaneous interfacial reaction between the different polyions leads to formation of polyelectrolyte complex membranes. Some of these have a very good performance in the membrane process pervaporation, especially for dehydration of organic liquids. The combination of a polyelectrolyte with an ionic surfactant of opposite charge results like‐wise membranes but with other separation properties. The differences between the two types of membranes, formed from cellulosesulfate in combination with cationic polyelectrolytes or cationic surfactants, will be discusse

ISSN:1022-1360    

DOI:10.1002/masy.19981260109

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe synthesis of polycations bearing reactive groups, namely tertiary anilines located in the side chain or in the main chain, is described. These polyions are employed in conventional alternating polyelectrolyte multilayer assembly or in a modified build‐up process including an azo coupling reaction on the topmost layer after every polycation adsorption step, which offers the potential to create multilayer structures with a non‐centrosymmetric structure. The characterization of these modified assemblies by UV/VIS spectroscopy reveals significant differences in the spectral data in dependence of the polycation struct

ISSN:1022-1360    

DOI:10.1002/masy.19981260110

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe processes proceeding at the contact of highly swollen lightly cross‐linked polyelectrolyte networks with aqueous solutions of oppositely charged linear polyions were studied. The reactions under discussion proceed as frontal processes and follow by strong (three orders of magnitude) contraction of the gel sample. The existence of sharp boundary between outer weakly swollen layer which is the reaction product—interpolyelectrolyte complex and the highly swollen inner part which is the initial unconverted gel is characteristic for the process. The kinetics of linear polyions absorption by polyelectrolyte networks and factors controlling the rate of sorption such as chemical structure of polyelectrolytes, nature and concentration of simple salts, pH, temperature were investigated. The “relay‐race” mechanism of linear polyelectrolyte transport was es

ISSN:1022-1360    

DOI:10.1002/masy.19981260111

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractInterpolyelectrolyte complexes (PECs) were obtained starting from polycations with (N,N‐dimethyl‐2‐hydroxypropylenammonium chloride) units in the main chain and sodium salts of the poly(acrylic acid), on one hand, and poly (2‐acrylamido‐2‐methylpropane sulfonic acid), on the other hand, as polyanions. The polycations were different as concerns both the content of the quaternary ammonium salt groups and the degree of branching. The polyanions were different both by their structure and molecular weight. The complex formation was followed through the variation of the reduced viscosity and of the conductivity of the reaction medium vs. the unit molar ratio polyanion/polycation in two ranges of co

ISSN:1022-1360    

DOI:10.1002/masy.19981260112

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY