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Flexible polymers at a solid-liquid interface : the adsorption of polyvinyl pyrrolidone onto silica
No full textWe undertook the present study in order to evaluate techniques which are devised to assess the comformations of adsorbed macromolecules. Since recent theories deal with these conformations, we also wanted to investigate to what extent these theories are supported by experimental data.In chapter 1 we outline the scope of this study and we give reasons for using polyvinyl pyrrolidone / silica as the model system.Chapter 2 deals with the general aspects of polymer adsorption. Some trends found from experimental work are mentioned, and the four main theories which have treated the problem of interacting chain molecules at a plane interface are briefly discussed. Arguments are presented which lead to the conclusion that, from a theoretical point of view, the best theory available at present is the one recently given by Scheutjens and Fleer (1979). However, it is shown that even this theory fails to take into account both the volume ratio between polymer and solvent and the flexibility of the polymer in a consistent way. We propose a simple way to modify the theory such that these properties are both incorporated; this requires the introduction of a new parameter into the theory: the segment-to-solvent volume ratio or bulkiness parameter b. A few calculations show how the results depend upon b. At the end of chapter 2 we also consider briefly the reversibility of polymer adsorption in connection with polydispersity effects.Chapter 3 presents a selection of relevant properties of the polymer, the solvents and the adsorbent.Adsorption experiments are discussed in chapter 4. Adsorbed amounts for two solvents (water and dioxane) are given as a function of chain length, properties of the adsorbent surface and polymer heterodispersity. It is found that PVP adsorbs strongly from both solvents, but in amounts that are substantially higher from dioxane than from water. Chapter 4 also deals with the desorption which occurs if suitable low molecular weight displacers are added to the solution. By means of a simple expression, the amount of displacer needed to just cause complete desorption is related to the strength with which the polymer is bound to the surface. With 5 different displacers an effective adsorption energy is estimated and its meaning is discussed. This type of measurements is entirely new in polymer adsorption studies. Although a detailed interpretation of the results is not straightforward, we obtain reasonable values for the adsorption energy parameter.Measurements of conformation parameters for adsorbed PVP are described in chapter 5. Bound fractions are determined spectroscopically (infrared, nuclear magnetic resonance) and completed with data from the literature (electron spin resonance). Calorimetry is used as a means to study the surface occupancy. The discrepancies between results from the various methods are considerable, and it is concluded that the techniques do not measure the same property. Nevertheless, the results are useful in gaining a further understanding of the adsorption phenomenon.In chapter 6 we compare in some detail experimental and theoretical results. The theory used is the aforementioned modification of the Scheutjens-Fleer theory and the experimental data comprise adsorbed amounts, bound fractions and interaction parameters. The adsorbed amounts, which can be fairly accurately measured, agree within 10 tot 20 % with the theoretically calculated values, over the whole molecular weight range. To our knowledge, this is the first time that quantitative agreement is obtained to such an extent. Bound fractions determined with ESR also agree fairly well with the theoretical values, and NMR gives a result in the right range. Infrared data lead to a serious underestimation of the bound fraction, which is easily explained on the basis of the chain structure. To a lesser extent, microcalorimetric results also tend to underestimate the bound fraction, although the results agree surprisingly well with enthalpies of wetting. The dependency on the solvent type is also correctly predicted.The conclusion is drawn that the introduction of the bulkiness parameter is an essential step towards a complete theory and that the modified Scheutjens-Fleer theory is strongly supported by experiment. Finally, we picture in some detail the conformation of adsorbed PVP, as it emerges from this study.<p/
The Visit of M. Cohen Stuart Was Reported in This Edition of De Hollander
Full text linkThe visit of M. Cohen Stuart was reported in this edition of De Hollander. He was warmly welcomed in the house of Dr. A. C. Van Raalte. Cohen Stuart preached in the First Reformed Church and in the college chapel. He came to Holland as a representative of the Dutch Alliance. Several members of the True Church were also in the building at night to listen to a few words spoken by somebody from another persuasion. On Monday, Van Raalte accompanied Cohen Stuart on a tour to the mouth of the Black Lake.https://digitalcommons.hope.edu/vrp_1870s/1182/thumbnail.jp
Cohen (Stuart A) Don-Yehiya (Eliezer) éds V. II: Conflict and Consensus in Jewish Political Life
No full textAzria Régine. Cohen (Stuart A) Don-Yehiya (Eliezer) éds V. II: Conflict and Consensus in Jewish Political Life. In: Archives de sciences sociales des religions, n°64/2, 1987. pp. 257-258
Cohen (Stuart A) Don-Yehiya (Eliezer) éds V. II: Conflict and Consensus in Jewish Political Life
No full textAzria Régine. Cohen (Stuart A) Don-Yehiya (Eliezer) éds V. II: Conflict and Consensus in Jewish Political Life. In: Archives de sciences sociales des religions, n°64/2, 1987. pp. 257-258
Elazar (Daniel J.) Cohen (Stuart A.) The Jewish Polity. Jewish Political Organization from Biblical Times to the Present
No full textAzria Régine. Elazar (Daniel J.) Cohen (Stuart A.) The Jewish Polity. Jewish Political Organization from Biblical Times to the Present. In: Archives de sciences sociales des religions, n°62/2, 1986. pp. 265-266
Elazar (Daniel J.) Cohen (Stuart A.) The Jewish Polity. Jewish Political Organization from Biblical Times to the Present
No full textAzria Régine. Elazar (Daniel J.) Cohen (Stuart A.) The Jewish Polity. Jewish Political Organization from Biblical Times to the Present. In: Archives de sciences sociales des religions, n°62/2, 1986. pp. 265-266
Camellia punctata Cohen Stuart 1916
No full text<p> <i>Camellia punctata</i> (Kochs) Cohen Stuart (1916: 66)</p> <p> ≡ <i>Thea punctata</i> Kochs (1900: 584).</p> <p> Type:— CHINA. Sichuan [Szechuan]: near Kangding [Tachienlu], 9000–13500 ft., December 1890, <i>A.E. Pratt 817</i> (<b>lectotype designated here:</b> K000380528!; isolectotypes: BM000611975!, E00284412!), Fig.1A.</p> <p> = <i>Camellia renshanxiangiae</i> C.X.Ye & X.Q.Zheng (2001: 160), <i>syn. nov.</i></p> <p> Type:— CHINA. Guangdong: Guangzhou, cultivated in the campus of Sun Yat-sen University, introduced from Yangshan, 10 March 2000, <i>C.X. Ye 5904</i> (holotype SYS00094790!; isotypes SYS00094786!, SYS00094787!, SYS00094788!, SYS00094789!, PE01598414!), Fig. 1B.</p> Nomenclatural notes <p> Kochs (1900) cited a single gathering <i>A.E. Pratt 817</i> in the protologue of <i>Thea punctata</i>, while, the corresponding herbarium was not specified. Three duplicates of this gathering were found in herbaria BM, E and K. The duplicate at K (000380528) with dissected flowers is in better condition, so it is selected as the lectotype.</p> <p> Cohen-Stuart (1916) transferred <i>Thea punctata</i> into <i>Camellia</i> on the page 66 in ‘ <i>Mededeelingen van het Proefstation voor Thee</i> ’, while Sealy (1958) misquoted the page number as 68, which was followed by subsequent scholars, such as Chang (1981), Chang & Bartholomew (1984), Chang & Ren (1998), Ming (2000), Ming & Bartholomew (2007).</p> Additional specimens of <i>C. punctata</i> examined <p> <b>CHINA. Sichuan</b>: sine loc. <i>S.N. Xu sn</i> (PE00629640); Cangxi, Huangmao, Huangnikan, ca. 710 m, 5 August 1965, <i>Z.Q. Chen 002</i> (CDBI); Chengdu, Longquan, Changsong Temple, ca. 1100 m, 27 May 1963, <i>X.Q. Li 037</i> (CDBI); the same locality, ca. 950 m, 28 April 1974, <i>W.G. Hu 108</i> (SZ); the same locality, ca. 550 m, 15 March 1979, <i>Sichuan vegetation Exp. 8279</i> (CDBI); Emei, <i>R.K. Zhao 29</i> (PE); Leshan [Chia-ting], 28 July 1928, 1500 ft., <i>W.P. Fang 2284</i> (E, K, PE); Wuyou Temple (Wuyussu), 24 July 1938, <i>W.P. Fang 12490</i> (BM, PE, SZ); the same locality, 3 March 1941, <i>L.Y. Tai 748</i> (PE); the same locality, 20 March 1941, <i>H.C. Chow 12911</i> (PE); the same locality, ca. 480 m, 11 November 2005, <i>S.X. Yang 1504, 1505, 1507</i> (KUN)); the same locality, ca. 335 m, 24 October 2018, <i>Y.L. Zhang, X.P. Li, G. Song et C.H. Li WYS181024-01-1</i> (CSH); San-e Mount., ca. 1700 m, 10 September 1959, <i>Z.T. Guan 6390</i> (PE). <b>Guangdong:</b> Guangzhou, cultivated in the campus of Sun Yat-sen University, 29 March 2006, <i>S.X. Yang 2121</i> (KUN); the same locality, 7 June 2012, <i>S.X. Yang 3820</i> (KUN).</p>Published as part of <i>Zhang, Ya-Li, Yu, Xiang-Qin, Jiang, Yin-Zi, Wu, Yin & Yang, Shi-Xiong, 2023, Camellia renshanxiangiae, a synonym of C. punctata (Theaceae), pp. 157-162 in Phytotaxa 609 (2)</i> on page 161, DOI: 10.11646/phytotaxa.609.2.9, <a href="http://zenodo.org/record/8272367">http://zenodo.org/record/8272367</a>
The Adsorption of Poly (vinyl-pyrrolidone) onto Silica. I. Adsorbed Amount
No full textThe adsorption of the flexible, linear, and nonionic homopolymer poly(vinyl pyrrolidone) from water and from 1,4-dioxane onto pyrogenic silica was studied. Results are reported for the adsorbed amount as a function of adsorption time, molecular mass, and molecular mass distribution (polydispersity). It is found that the adsorption of fractionated samples can be qualitatively explained by the recent theory of Scheutjens and Fleer. However, the influence of the solvent type is larger than predicted by this theory, and an extension of the model to account for this influence is suggested. The polydispersity effects encountered in adsorption isotherms are satisfactorily accounted for by a theory published by Cohen Stuart, Scheutjens, and Fleer
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Supramolecular perspectives in colloid science
No full textSupramolecular chemistry puts emphasis on molecular assemblies held together by non-covalent bonds. As such, it is very close in spirit to colloid science which also focuses on objects which are small, but beyond the molecular scale, and for which other forces than covalent bonds are crucial. We discuss in this review the preparation and properties of new colloidal systems which borrow on the one hand from classical topics in colloid science, such as micellization, and on the other hand from concepts in supramolecular chemistry, such as reversible supramolecular polymers
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