摘要:

AbstractThe subject is of importance in a variety of colloidal and biological problems. It includes (a) adsorption on solid surfaces, (b) the equation of state of mono or multilayers on liquid interfaces, (c) surface tension of solutions. There are two aspects, namely the molecular configurations at the interface and the resulting contributions to the free energy. Assume the surface to be a regular array of adsorbing sites, each accommodating one chain segment. Unless the segment‐site interaction is extremely large in comparison withkTand of long range, flexible chains will not deposit completely. H. L. Frisch and the author have previously shown for random coils that the average numbervof segments adsorbed out of a total oftper chain is proportional tot1/2and increases with chain flexibility and thus temperature in a good solvent. They also established the consequences of this for (a) and (b). The present discussion, based on work in collaboration with Frisch, includes surface tension and differs from our earlier results at low surface concentration θ. As previously, the treatment neglects fluctuations inv, which are small for larget. The isotherm in dilute solutions is essentially θ/[v(1 − θ)v] =Kc, whereKis a function ofv,T, depending on the properties of the bulk polymer and solvent and increasing with molecular weight. Deviations from a Langmuir isotherm are less pronounced than for rigid molecules. The second virial coefficient of the pressurearea curve depends on the ratiov/tand hence on molecular weight and flexibility differently from a completely deposited molecule, flexible or rigid. The limiting change in surface tension depends on two‐opposing terms. When adsorption is sufficiently strong, a decrease proportional toK, and hence increasing with molecular weight, results. This competes with an increase proportional tov/t∝t−1/2, arising from the activity of

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202911901

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractAn apparatus has been constructed for measuring rapidly the coefficient of restitution by impact of a steel ball on samples of polymers as a function of temperature. Such measurements are described as rebound relaxation “spectra,” the energyEabsorbed on impact being plotted against temperatureT. The main absorption peak corresponds to the dynamic second order transition. First‐order transitions give anS‐shapedE–Tplot. The validity and sensitivity of the technique are illustrated with rebound spectra of amorphous and crystalline linear polymers as well as crosslinked resins. The kinetics of various “curing” (crosslinking) reactions are followed in terms of the displacement of the second order transition peak towards higher temperatures. Where such a curing reaction approaches an equilibrium (or pseudo‐equilibrium), the observed kinetics are interpretable on the theory of relaxation processes. For this purpose, the displacement of the peak may be charted fromisothermalmeasurements ofE. A more significant technique usesisoelasticmeasurements of the peak displacement,i.e., measurements of the change with time of the temperature required to keep the rebound height constant. The isothermal approach of the peak to its equilibrium value is a typical Maxwellian (first order) rate process. The isoelastic approach to equilibrium atconstantrebound producesconstantrates of peak displacement over big temperature ranges. This is explained qualitatively because elastic rebound and chemical crosslinking are both dependent on the molecular relaxation rate of chain segments. The theory is illustrated with the curring reactions of expoxide, polyester, urea‐formaldehyde, and phenol‐formaldehyde resins. The epoxide system studied behaves as a “conservative” system, in which the rate of cure is dependent on the state of cure and the temperature, but not on the curing schedule by which that state of

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202911902

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractHeats and entropies of dilution of dilute solutions (concentration range 0.2–1.0 g./100 ml.) of cellulose acetate, ethyl cellulose, and cellulose nitrate, of similar degrees of substitution and polymerization, in a number of representative solvents, have been obtained from temperature coefficients of osmotic pressure. In some cases, degradation of polymer at the higher temperature used seems possible and an attempt is made to allow for this in the estimation of values of ΔH̄1and ΔS̄1. Heats of dilution for the cellulose acetate and ethyl cellulose systems are generally endothermal, those for the cellulose nitrate systems being exothermal. Entropies of dilution are less than those obtained for comparable systems containing less polar and more flexible polymers. Those for the cellulose nitrate systems do not differ much from “ideal” values. The value of ΔH̄1/ϕ22, where ϕ2is the volume fraction of polymer calculated from the density of the bare polymer, for each cellulose acetate system and most of the ethyl cellulose systems seems to be effectively independent of concentration. Values for the cellulose nitrate systems seems to be effectively independent of concentration. Values for the cellulose nitrate systems become less negative as the concentration increases. Values of ΔH̄1for the cellulose acetate and ethyl cellulose systems are generally in the order to be expected from the solubility parameters of the solvents and polymers. ΔS̄1/ϕ22may vary with concentration in a manner rather similar to that suggested by simpler lattice theories. These results are tentatively interpreted in terms of solvation of polymer and possible endothermal mixing of solvated polymer and solvent. Although values of the entropy contribution to the interaction parameter χ1for the cellulose acetate and ethyl cellulose systems are not always inagreement with the predictions of simpler lattice theories it is possible, if solvation, segment size, and chain stiffness are allowed for, that the thermodynamic properties of dilute solutions of cellulose derivatives may be at least qualitatively interpreted in ter

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202911903

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe behavior of human serum albumin in acid solutions containing chloride ions and in citrate and acetate buffers of pH 1 to 5 has been investigated by the method of light scattering. The reduced intensity of the scattered light was found to increase with decreasing pH: this change is most marked in acetate buffers, somewhat less marked in citrate, less again in the presence of higher concentrations of sodium chloride, and least in solutions of low ionic strength and in water. The phenomenon cannot be ascribed to the presence of lipoid substances alone: the possibility of complex formation must also be taken into account.

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202911904

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe density of like‐charged groups distributed along the molecules of proteins is much lower than in molecules of polyelectrolytes. From this it follows that the degree of deformation of the protein molecules resulting from the charge is much less. In buffered solutions—if the correction for hydration (measured by the compressibility method) is taken into account—the shape of gelatin particles (as measured by viscosity) practically does not depend on the pH, while in unbuffered solutions it varies roughly in proportion to the fourth to fifth root of the number of charges. For molecules of serum albumin and egg albumin the deformation is proportional to the 25th to 30th root of the number of charges,i.e., completely negligible. This comparison also shows that the deformation of the threadlike molecules of gelatin occurs much more easily than with the firmly molecules of the globular proteins. For globular proteins the following expression has been derived\documentclass{article}\pagestyle{empty}\begin{document}$$ E = \frac{{1.37 \times 10^3 n^{{\raise0.7ex\hbox{$3$} \!\mathord{\left/ {\vphantom {3 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}} m^{{\raise0.7ex\hbox{$2$} \!\mathord{\left/ {\vphantom {2 3}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$3$}}} }}{{S^{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}} a_0^2 b_0 \left( {m^{{\raise0.7ex\hbox{$2$} \!\mathord{\left/ {\vphantom {2 3}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$3$}}} - 1} \right)^2 }}\exp \left\{ { - \kappa /\sqrt {{n \mathord{\left/ {\vphantom {n S}} \right. \kern-\nulldelimiterspace} S}} } \right\} $$\end{document}whereEis the modulus of elasticity,nthe number of charges inthe molecule,mthe relative elongation of the molecule,a0,b0, andSthe semi‐axes and surface of the ellipsoidal molecule and κ the reciprocal thickness of the ionic atmosphere. A value ofE= 10–40 kg./mm.2was calculated according to this relation for the molecules of these globular proteins (for soft rubberE= 0.14 kg./mm.2, for polyamides 70–80 kg./mm.2, for ebonite 50–80 kg./mm.2, etc.). These results for the first time quantitatively characterize the high rigidity of the molecules of glo

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202911905

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractIn the study of thermal diffusion of high polymers in a solvent, instruments are commonly used which have a lower and upper chamber. The thermal diffusion effect causes an increase of concentration in the lower chamber and, conversely, a decrease in the upper one. Simultaneous changes in the average molecular weights occur in both chambers, and, in agreement with theory, the average molecular weight in the lower chamber increases. In our experiments we found that the average molecular weight first increases in the upper chamber, reaches a maximum, and then decreases to values even below the initial value. The opposite occurs in the lower chamber. This phenomenon of “inversion” must be taken into account in studying the applicability of thermal diffusion for obtaining distribution curves. We are also attempting to use it directly for separating fractions of lower molecular wei

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202911906

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractL'influence de la concentration sur la biréfringence d'écoulement des solutions de desoxyribonucléate de sodium est étudiée pour divers échantillons d'ADN. Lors du gonflement dans NaCl molaire du gel d'ADN obtenu par précipitation alcoolique, l'ADN se dissout progressivement. Des prélèvements successifs permettent de séparer des fractions qui diffèrent par leurs propriétés en solution diluée. Certaines fractions, principalement celles d'extraction précoce, présentent, aux très faibles concentrations, des anomalies de biréfringence d'écoulement. C'est ainsi qu'à gradient de vitesse constant l'angle d'extinction χ et le facteur optique ψ augmcntent de façon anormalement rapide avec la dilution dès que la concentration devient inférieure à 2 × 10−5g/ml. Dans les conditions de l'expérience, les particules d'ADN sont pratiquement indéformables; les variations de χ et de ψ. semblent donc indiquer, aux grandes dilutions, une importante diminution de la taille des particiilrs et une augmentation de leur anisotropie. Au contraire, avec les fractions d'extraction tardive, l'augmentation d'anisotropie est souvent accompagnée d'un accroissement apparent de taille. Par contre, avec les mêmes échantillons d'ADN et dnns le même domaine de concentration, la visrosimétric et l'ultracentrifugation ne mettent pas d'anomalir en évidence, d'où une apparente contradiction. La question est discutée tie savoir si les effets observés en biréfringence d'écoulement peuvent être ou non imputés à des intcractions entre les molécules dissoutes. On recherche aussi quel modèle de particule peut être simultanénent compatible avec les résultats de la biréfringence d'écodement, de la viscosité et de la sédimentation, compte tenu des données récentes sur la structure de l'ADN. Certaincs contradictions semblant difficilement réductibles, on est conduit à suggerer l'éventuelle nécessité de reconsiderér la signification physique des grandeurs mesurées et des divers paramètres utilisés pour caractériser les particu

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202911907

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractLe bromure de polyvinyle a été préparé par photopolymérisation et la masse moléculaire des fractions a été mesurée par diffusion de la lumière. Nous avons étudié l'absorption diélectrique pour comparer les variations des composantes du pouvoir inducteur spécifique de ce polyère en solution dans deux solvants en fonction de la fréquence du champ électrique comprise entre 1 et 32 MHz et de la température. Une étude analogue a été faite sur le chlorure de polyvinyle. Nous avons interprété les temps de relaxation et les énergies d'activatio

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202911908

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe second virial coefficients of two polymethylmethacrylate fractions of M̄w= 1.18 × 106and 9.2 × 104and a series of mixed fractions from them have been measured by osmotic pressure and by light scattering in acetone at 25°C. The results show thatA 2′is practically insensitive to an admixed lower molecular weight component but very sensitive to any higher molecular weight component contained in the sample. On the contrary,A2is sensitive to the lower molecular weight component as well as to the higher molecular weight component present. The values ofA2andA 2′for the mixed fractions, estimated according to the theory of Flory and Krigbaum, show agreement in the general character of theA2‐ andA 2′‐composition curves. A broad maximum occurs on theA2‐composition curve around 20% of the higher molecular weight fraction, while a rather sharp maximum occurs on theA 2′‐composition curve around 6% of the highe

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202911909

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractLa relation entre la viscosité intrinsèque et la masse moléculaire de molécules à chaîne courte fait l'objet du présent travail. Une relation du type\documentclass{article}\pagestyle{empty}\begin{document}$$ [\eta ] = A + KM^a $$\end{document}rend compte des résultats expérimentaux dans le cas des polyoxyéthylhe glycols dans tout le domaine de masses moléculaires considéré. Par contre la viscosité intrinsèque des α,ω‐diméthoxy polyéthylèneglycols diffère de celle des polyoxyéthylène glycols correspondants de façon assez notable dans le domaine des masses moléculaires faibles. Le raccordement satisfaisant des courbes [η] =f(M) relatives aux deux séries de substances nous incite à admettre d'une façon générale, dans le domaine de masses moléculaires considéré, une loi de viscosité de la forme:\documentclass{article}\pagestyle{empty}\begin{document}$$ [\eta ] = f\left( M \right) + KM^a $$\end{document}dans laquelle le premier terme est en rapport avec la nature chimique de la chaine et le deuxième résu

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202911910

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY