Comparative Thermodynamic Behavior of Physically Restricted Cyclohexane and Cyclohexanone in Porous Silica

1998 ◽  
Vol 543 ◽  
Author(s):  
S. Amanuel ◽  
V. M. Malhotra
Keyword(s):  
Transition Temperature ◽  
Thermodynamic Properties ◽  
Differential Scanning Calorimeter ◽  
Pore Radius ◽  
Porous Silica ◽  
Melting Transition ◽  
Confined Fluids ◽  
Bulk Fluid ◽  
Host Interactions ◽  
Dsc Measurements

AbstractWe undertook comparative differential scanning calorimeter (DSC) measurements on cyclohexane (C6H12) and cyclohexanone (C6H10O), physically confined in porous silica of pore radius 4, 7.5, 15, 30, and 62.5 nim, with a view to ascertain how guest fluid-surface host interactions affected the thermodynamic properties of the confined fluids. Our results can be summarized as follows: (a) No distinct signature of freezing or melting transition was observed for the physically confined cyclohexanone, irrespective of whether the bulk was present outside the pores. However, this was not the case for cyclohexane. (b) The solid-to-solid transition temperature of cyclohexane and cyclohexanone inversely scaled with the pore radius of the host porous silica. (c) The cubic-to-orthorhombic transition of cyclohexanone was strongly influenced by whether the bulk fluid was present outside the pores. In the absence of the bulk, the transition temperature was considerably suppressed relative to the bulk transition temperature. However, in the presence of the bulk, the confined and the bulk transitions occurred at the same temperature.

Effects of Surfaces on the Melting/Freezing Behavior of Fluids in Derivatized- and Nude-Porous Silica

1992 ◽  
Vol 290 ◽  
Author(s):  
V. K. Malhotra ◽  
R. Mu ◽  
A. Natarajan
Keyword(s):  
Differential Scanning Calorimetry ◽  
Surface Structure ◽  
Pore Radius ◽  
Porous Silica ◽  
Freezing Behavior ◽  
Melting Transition ◽  
Scanning Calorimetry ◽  
Thermodynamic Behavior ◽  
Dsc Measurements ◽  
Effective Pore Radius

AbstractComparative differential scanning calorimetry (DSC) measurements were made at 200 K < T < 310 K on geometrically restricted cyclohexane and n-decane in nude-, trimethyl derivatized-, and hexyl derivatized-porous (Rp = 4 nm) silica with a view to determine how the surface structure of the confining media affects the thermodynamic behavior of the restricted fluid. Our results suggest that, irrespective of the fact that both trimethyl derivatized- and hexyl derivatized-silica have methyl terminal groups, the freezing or melting transition of cyclohexane is much more depressed in trimethyl derivatized-silica than in hexyl derivatized- or nude-silica. This is not the case for n-decane where the depression in the melting transition is consistent with the fact that the effective pore radius of the hexyl derivatized-silica is smaller than the trimethyl derivatized- or nude-silica.

Freezing/Melting Transition of Physically Restricted n-Decane

1994 ◽  
Vol 366 ◽  
Author(s):  
P. M. Hoffmann ◽  
V. M. Malhotra
Keyword(s):  
Large Fraction ◽  
Porous Silica ◽  
Melting Transition ◽  
Scanning Calorimetry ◽  
Freezing Transition ◽  
Dsc Measurements ◽  
Linear Behavior ◽  
Alkane Chain ◽  
Two Peaks ◽  
Interesting Behavior

ABSTRACTWe undertook differential scanning calorimetry (DSC) measurements at 170 K < T < 300 K on n-decane, physically confined in 8 nm (= diameter D) porous silica derivatized with various functional groups, to understand how surface structure of the confining media affects the freezing or melting transition of the n-decane. Though we observed a typical depression (ΔT) in the freezing or melting transition temperature of the physically confined decane, our results failed to manifest usual linear dependence of ΔT on D−1 when the expected contraction in D, due to the presence of aminopropyl-, hexyl-, phenyl- or trimethyl-groups on the silica surface, was taken into account. However, it is worth noting that a linear behavior was observed between ΔT and D−1 if only alkane-chain derivatized hosts were considered. Our results also indicate that a large fraction of physically confined n-decane (35 to 70 %), depending on the host silica, does not participate either in the melting or freezing transition. The most interesting behavior observed in the present study is the occurrence of the unusual two peaks associated with the freezing transition of physically confined decane. This bimodal behavior is strongly dependent on the chemistry of the confining silica host's surface.

Normal-Strain Induced Change in Lattice-Type for Confined Cyclohexane Films

1996 ◽  
Vol 464 ◽  
Author(s):  
J.E. Curry ◽  
J.H. Cushman
Keyword(s):  
Triangular Lattice ◽  
Chemical Potential ◽  
Potential Temperature ◽  
Computer Experiments ◽  
Square Lattice ◽  
Melting Transition ◽  
Normal Strain ◽  
Surface Forces Apparatus ◽  
Bulk Fluid ◽  
Lattice Type

ABSTRACTOne to three layer cyclohexane films confined between mica-like surfaces are studied to elucidate changes in the films' lattice-type. The laterally confined film is in equilibrium with the bulk fluid that is well into the liquid regime of its phase diagram. Monte Carlo simulations are conducted at constant chemical potential, temperature, and V=Ah, where A is the lateral area and h is the separation between the walls. One and two layers of fluid freeze as h increases. The one layer fluid has a triangular lattice, while the two layer fluid exhibits first a square lattice and then a triangular lattice with increasing surface separation. In contrast to previous studies, solidlike order is induced primarily by the strong fluid-solid interaction and is largely a function of pore width. A shift in the relative alignment of the surfaces perturbs the solidlike fluid structure but does not cause the sudden shear melting transition associated with epitaxial alignment of the fluid atoms with the surface. There is a correlation between the shear stress calculated in the computer experiments and that measured in Surface Forces Apparatus experiments.

Preparation of Poly(aniline-co-phenol) and Study Its Properties and Its Polymerization Kinetics Using Two Methods: UV-Vis and HPLC

2021 ◽  
Vol 43 (5) ◽  
pp. 505-505
Author(s):  
Juhaina Alghdir and Ahmad Falah Juhaina Alghdir and Ahmad Falah
Keyword(s):  
Transition Temperature ◽  
Reaction Order ◽  
Sem Analysis ◽  
304 Stainless Steel ◽  
Melting Transition ◽  
Gravimetric Analysis ◽  
Zero Order Reaction ◽  
Kinetics Of ◽  
Thermal Stability Of ◽  
Poly Aniline

The co-polymerization of polyaniline is one of the most important methods used to improve the electrical activity and thermal stability of polyaniline. Previously, electrochemical co-polymerization of phenol and aniline was performed on 304 stainless steel anodes. In this study, we present the co-polymerization of aniline and phenol chemically at laboratory temperature in an acidic medium with ammonium pyrosulfate as an oxidant. The Scanning Electron Microscopy (SEM) analysis of poly(aniline-co-phenol) sample shows a rough (non-smooth) surface with crystalline particles with microscopic diameters. We characterized the prepared polymer with DSC, DTA, and thermos gravimetric analysis (TGA). We found that the thermal decomposition of poly(aniline-co-phenol) was on six steps. The glass transition temperature of the co-polymer (Tg) was found at 863.89 and#176;C and the melting transition temperature was observed at 877.80 and#176;C. We studied the kinetics of Poly(aniline-co-phenol) using two methods: UV-Vis, HPLC. Then we determined the reaction order. It was found that the reaction was the zero-order reaction (n=0) in both previous two methods.

scholarly journals Differential Scanning Calorimetry for Determining the Thermodynamic Properties of Selected Honeys

2015 ◽  
Vol 59 (1) ◽  
pp. 109-118 ◽  
Author(s):  
Jolanta Tomaszewska-Gras ◽  
Sławomir Bakier ◽  
Kamila Goderska ◽  
Krzysztof Mansfeld
Keyword(s):  
Differential Scanning Calorimetry ◽  
Heat Capacity ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Thermodynamic Properties ◽  
Sugar Content ◽  
Scanning Calorimetry ◽  
Glass Transition Temperatures ◽  
Complete Liquefaction

Abstract Thermodynamic properties of selected honeys: glass transition temperature (Tg), the change in specifi c heat capacity (ΔCp), and enthalpy (ΔH) were analysed using differential scanning calorimetry (DSC) in relation to the composition i.e. water and sugar content. Glass transition temperatures (Tg) of various types of honey differed significantly (p<0.05) and ranged from -49.7°C (polyfloral) to -34.8°C (sunflower). There was a strong correlation between the Tg values and the moisture content in honey (r = -0.94). The degree of crystallisation of the honey also influenced the Tg values. It has been shown that the presence or absence of sugar crystals influenced the glass transition temperature. For the decrystallised honeys, the Tg values were 6 to 11°C lower than for the crystallised honeys. The more crystallised a honey was, the greater the temperature difference was between the decrystallised and crystallized honey. In conclusion, to obtain reliable DSC results, it is crucial to measure the glass transition after the complete liquefaction of honey.

The Influence of Gamma Radiation on the Glass Transition of Hydroxyapatite/Poly L-Lactide Composite

2007 ◽  
Vol 555 ◽  
pp. 497-502
Author(s):  
Dejan Miličević ◽  
S. Trifunović ◽  
N. Ignjatović ◽  
E. Suljovrujić
Keyword(s):  
Activation Energy ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Structural Relaxation ◽  
Absorbed Dose ◽  
Gel Permeation Chromatography ◽  
Chain Scission ◽  
Scanning Calorimetry ◽  
Dsc Measurements

Hydroxyapatite/poly L-lactide (HAp/PLLA) is a composite biomaterial which has been widely utilized for substitution and reparation of the hard bone tissue. It is well known that gamma irradiation has been successfully employed in the modification/sterilization of such porous composites and that it has advantages over other procedures. In this study, differential scanning calorimetry (DSC) measurements were made to investigate the influence of the radiation on glass transition behavior and structural relaxation, as well as to estimate the activation energy for this process. The apparent activation energy ΔH* for structural relaxation in the glass transition region was determined on the basis of the heating rate dependence of the glass transition temperature Tg. Furthermore, the results were correlated with those obtained by gel permeation chromatography (GPC). Our findings support the fact that the radiation-induced chain scission in the PLLA phase is the main reason for the decrease of the glass transition temperature and/or activation energy with the absorbed dose.

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