scholarly journals Poly(N,N′-Diethylacrylamide)-Based Thermoresponsive Hydrogels with Double Network Structure

Polymers ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2502
Author(s):  
Lenka Hanyková ◽  
Ivan Krakovský ◽  
Eliška Šestáková ◽  
Julie Šťastná ◽  
Jan Labuta
Keyword(s):  
Thermal Sensitivity ◽  
Bound Water ◽  
Temperature Response ◽  
Scanning Calorimetry ◽  
Critical Temperatures ◽  
Double Network ◽  
Volume Transition ◽  
Enthalpy And Entropy Changes ◽  
Enthalpy And Entropy ◽  
Hydrophilic Network

Temperature response of double network (DN) hydrogels composed of thermoresponsive poly(N,N′-diethylacrylamide) (PDEAAm) and hydrophilic polyacrylamide (PAAm) or poly(N,N′-dimethylacrylamide) (PDMAAm) was studied by a combination of swelling measurements, differential scanning calorimetry (DSC) and 1H NMR and UV-Vis spectroscopies. Presence of the second hydrophilic network in DN hydrogels influenced their thermal sensitivity significantly. DN hydrogels show less intensive changes in deswelling, smaller enthalpy, and entropy changes connected with phase transition and broader temperature interval of the transition than the single network (SN) hydrogels. Above the transition, the DN hydrogels contain significantly more permanently bound water in comparison with SN hydrogels due to interaction of water with the hydrophilic component. Unlike swelling and DSC experiments, a rather abrupt transition was revealed from temperature-dependent NMR spectra. Release study showed that model methylene blue molecules are released from SN and DN hydrogels within different time scale. New thermodynamical model of deswelling behaviour based on the approach of the van’t Hoff analysis was developed. The model allows to determine thermodynamic parameters connected with temperature-induced volume transition, such as the standard change of enthalpy and entropy and critical temperatures and characterize the structurally different states of water.

scholarly journals Direct measurement of enthalpy and entropy changes in NH3 promoted O2 activation over Cu‐CHA at low temperature

ChemCatChem ◽  
2021 ◽  
Author(s):  
Xueting Wang ◽  
Lin Chen ◽  
Peter N. R. Vennestrøm ◽  
Ton V. W. Janssens ◽  
Jonas Jansson ◽  
...  
Keyword(s):  
Low Temperature ◽  
Direct Measurement ◽  
O2 Activation ◽  
Entropy Changes ◽  
Enthalpy And Entropy Changes ◽  
Enthalpy And Entropy

Thermodynamics of Protonation and Sodium Binding of Sulfate in Concentrated NaCl and CsCl Solutions Studied by Raman Spectroscopy

2000 ◽  
Vol 53 (5) ◽  
pp. 363 ◽  
Author(s):  
Steven Kratsis ◽  
Glenn Hefter ◽  
Peter M. May ◽  
Pal Sipos
Keyword(s):  
Raman Spectroscopy ◽  
Excellent Agreement ◽  
Thermodynamic Data ◽  
Association Constant ◽  
Protonation Constant ◽  
Ion Pairing ◽  
Ion Pair ◽  
Enthalpy And Entropy Changes ◽  
Enthalpy And Entropy ◽  
Sodium Binding

The protonation constant (pKa) of SO42–(aq) has been determined at ionic strengths 0.5 M ≤I ≤4.0 M in NaCl and CsCl media at 25˚C by using Raman spectroscopy. These data were used to calculate the association constant of the NaSO4–(aq) ion pair in CsCl media. The results are in excellent agreement with previous values obtained by other techniques. The (pKa) was also measured at I = 4 M in both media at temperatures up to 85˚C and the associated enthalpy and entropy changes were calculated. However, reliable thermodynamic data for the ion-pairing reaction could not be obtained at higher temperatures probably because of competition from CsSO4–(aq).

Studies on Bound Water of Cellulose by Differential Scanning Calorimetry

1981 ◽  
Vol 51 (9) ◽  
pp. 607-613 ◽  
Author(s):  
Kunio Nakamura ◽  
Tatsuko Hatakeyama ◽  
Hyoe Hatakeyama
Keyword(s):  
Differential Scanning Calorimetry ◽  
Bound Water ◽  
Scanning Calorimetry

Extrem asymmetrisch gebundene Wassermoleküle-Kristallstrukturen von Sr(OH)Cl · 4 H2O, Sr(OH)Br · 4 H2O und Ba(OH)I·4 H2O / Extremely Asymmetrically Bound Water Molecules-Crystal Structures of Sr(OH)Cl · 4 H2O, Sr(OH)Br · 4 H2O, and Ba(OH)I·4 H2O

1991 ◽  
Vol 46 (10) ◽  
pp. 1279-1286 ◽  
Author(s):  
Thomas Kellersohn ◽  
Konrad Beckenkamp ◽  
Heinz Dieter Lutz
Keyword(s):  
Crystal Structures ◽  
Bound Water ◽  
Structure Type ◽  
Water Molecules ◽  
Halide Ions ◽  
Weak Hydrogen Bond ◽  
Scanning Calorimetry ◽  
Unknown Structure ◽  
Stretching Vibrations ◽  
Strong Distortion

The crystal structures of isotypic Sr(OH)Cl ·4 H2O, Sr(OH)Br·4 H2O, and Ba(OH)I·4 H2O are reported. The title compounds crystallize in a hitherto unknown structure type, space group PĪ, Z = 2. The final R values obtained are 0.0261, 0.069, and 0.062, respectively. The coordination of the metal ions is monocapped square antiprismatic with 7 H2O, 1 OH- and 1 halide ion. The halide ions separate metal/water/hydroxide layers. Each of the four crystallographically different water molecules serves as donor for one very strong and one very weak hydrogen bond and, hence, is extremely asymmetrically bound. Owing to this strong distortion, the largest one known so far, the OH stretching vibrations of the H2O molecules are intramolecularly decoupled as shown from vibrational spectra. The enthalpies of dehydration obtained from differential scanning calorimetry are reported.

scholarly journals Studies on the Maximum Bound Water Content by the Differential Scanning Calorimetry on Lipstick

2012 ◽  
Vol 38 (3) ◽  
pp. 197-200
Author(s):  
Khee-Hwan Choi ◽  
Myung-Jin Ann ◽  
Hong-Ha Son ◽  
Kyong-Seub Kim ◽  
Sang-Min Lee ◽  
...  
Keyword(s):  
Differential Scanning Calorimetry ◽  
Water Content ◽  
Bound Water ◽  
Scanning Calorimetry ◽  
Bound Water Content

scholarly journals A THERMODYNAMIC ANALYSIS OF MITOTIC SPINDLE EQUILIBRIUM AT ACTIVE METAPHASE

1973 ◽  
Vol 57 (1) ◽  
pp. 133-147 ◽  
Author(s):  
R. E. Stephens
Keyword(s):  
Growth Conditions ◽  
Pool Size ◽  
Polarization Microscopy ◽  
Dissociation Kinetics ◽  
Mitotic Apparatus ◽  
Enthalpy And Entropy Changes ◽  
Enthalpy And Entropy ◽  
Best Fit ◽  
Two Temperature ◽  
Direct Immersion

The mitotic apparatus of first-division metaphase eggs of the sea urchin Strongylocentrotus drobachiensis was observed by means of polarization microscopy under controlled temperature conditions. Eggs were fertilized and grown at two temperature extremes in order to produce two different sizes of available spindle pool. Slow division time allowed successive samples of such cells to be observed at the same point in metaphase but at different equilibrium temperatures, yielding curves of metaphase equilibrium birefringence vs. observational temperature. Using the plateau value of birefringence at higher temperatures as a measure of total available spindle pool and the observed birefringence at lower temperatures as a measure of polymerized material at equilibrium, the spindle protein association was evaluated according to the method of Inoué. Both pool conditions produced linear van't Hoff functions. Analysis of these functions yielded enthalpy and entropy changes of +55–65 kcal/mol and +197–233 entropy units (eu), respectively. These values for active mitotic metaphase are quite comparable to those obtained by Inoué and co-workers for arrested meiotic metaphase cells. When other equilibrium treatments were considered, the best fit to the experimental data was still that of Inoué, a treatment which theoretically involves first-order polymerization and dissociation kinetics. Treatment of metaphase cells with D2O by direct immersion drove the equilibrium to completion regardless of temperature, attaining or exceeding a birefringence value equal to the cell's characteristic pool size; perfusion with D2O appeared to erase the original temperature-determined pool size differences for the two growth conditions, attaining a maximum value characteristic of the larger pool condition. These data confirm Inoué's earlier contention that D2O treatment can modify the available spindle pool.

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