scholarly journals Hysteresis Effects During the Phase Transition in Solutions of Temperature Sensitive Polymers

2017 ◽  
Vol 19 (1) ◽  
pp. 41 ◽  
Author(s):  
I.E. Suleimenov ◽  
O. Guven ◽  
G.A. Mun ◽  
Ch. Uzun ◽  
O.A. Gabrielyan ◽  
...  

It is demonstrated, for the first time,that well-known phase transitions induced by changes in temperature in solutions of polymers containing both hydrophilic and hydrophobic functional groups could be followed by noticeable hysteresis effects. A<br />well-known phase transitions accompanied by a sharp change in fluid properties, in particular its optical density can be induced by many external influences, including temperature changes occurring in the solutions of polymers containing both<br />hydrophilic and hydrophobic functional groups. Since intensification subsequent hydrophobic interactions, leading to loss of solubility of the polymer molecules, resulting, in particular, a significant increase in the turbidity of the medium and are accompanied by a pronounced hysteresis phenomena. Hysteresis phenomena in the processes of molecular-scale play an important theoretical and practical interest in linkage with the development of advanced nano-level technology. In particular, the issue of the development of molecular "trigger" switches, and other analog electronic systems, implemented on submolecular level was actively discussed. In fact, under the same physical conditions of the environment of macromolecules system can be in two different states, which resolves the issue of programming such molecules. State of these polymers depends on their way of formation and thermodynamic variables. Observed effect could be utilized directly for information recording into the structure on the basis of stimulus-sensitive macromolecular chains. In fact, it is a first step towards creating memory of quasi-biological elements.

1952 ◽  
Vol 5 (2) ◽  
pp. 288
Author(s):  
RG Wylie

Hysteresis phenomena associated with the adsorption of gases on solid surfaces are usually explained in terms of three-dimensional capillary effects or with more or less unspecific reference to phase transitions. It is shown that hysteresis effects are to be expected when two dimensional phase transitions occur on solids. In the connection, the thermodynamic equation governing the equilibrium of small, incompressible two-dimensional phases is derived. Such phases can form on an imperfect solid surface in an irreversible manner and, as calculation shows, can contribute significantly to the hysteresis of adsorption. In some cases the phase change may be responsible for the whole effect. The diffuseness of first-order phase transitions may be due to the same mechanism.


2014 ◽  
Vol 136 (9) ◽  
Author(s):  
Giti Karimi-Moghaddam ◽  
Richard D. Gould ◽  
Subhashish Bhattacharya

This paper presents results from theoretical and numerical studies of a single-phase, temperature sensitive magnetic fluid operating under steady-state laminar flow conditions in a partially heated thermomagnetic circulation loop under the influence of an external magnetic field (created by a solenoid). A one-dimensional theoretical model has been developed using scaling arguments to characterize thermomagnetic circulation in this loop in terms of the geometric length scales, magnetic fluid properties, and the strength of the imposed magnetic field. In parallel to this theoretical analysis, supporting numerical simulations using Comsol Multiphysics simulation software have been undertaken to obtain data for use in this 1D model. Comparison between experimental data and numerical simulation results and also a grid sensitivity analysis was carried out to validate the numerical simulation. A correlation for the nondimensional heat transfer (Nusselt number) as a function of the appropriate magnetic Rayleigh number and a correlation for the mass flow rate based on the system's properties are developed.


Author(s):  
Giti Karimi-Moghaddam ◽  
Richard D. Gould ◽  
Subhashish Bhattacharya

This paper presents results from theoretical and numerical studies of a single-phase, temperature sensitive magnetic fluid operating under steady-state laminar flow conditions in a partially heated thermomagnetic circulation loop under the influence of an external magnetic field (created by a solenoid). A one-dimensional theoretical model has been developed using scaling arguments to characterize thermomagnetic circulation in this loop in terms of the geometric length scales, magnetic fluid properties, and strength of the imposed magnetic field. In parallel to this theoretical analysis, supporting numerical simulations using COMSOL Multiphysics simulation software have been undertaken to obtain data for use in this 1D model. A correlation for the non-dimensional heat transfer (Nusselt number) as a function of the appropriate magnetic Rayleigh number and a correlation for the mass flow rate based on the system’s properties are developed.


Gels ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 16
Author(s):  
Nur Sena Okten Besli ◽  
Nermin Orakdogen

A convenient method for the preparation of polybasic ternary hybrid cryogels consisting of Halloysite nanotubes (HNTs) and tertiary amine functional groups by freezing-induced gelation is proposed. Ternary hybrid gels were produced via one-shot radical terpolymerization of 2-hydroxyethyl methacrylate (HEMA), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), and DEAEMA in the presence of HNTs. The equilibrium swelling in various swelling media and the mechanical properties of the produced ternary hybrid gels were analyzed to investigate their network structure and determine their final performance. The swelling ratio of HNT-free gels was significantly higher than the ternary hybrid gels composed of high amount of HNTs. The addition of HNTs to terpolymer network did not suppress pH- and temperature-sensitive behavior. While DEAEMA groups were effective for pH-sensitive swelling, it was determined that both HEMA and DEAEMA groups were effective in temperature-sensitive swelling. Ternary hybrid gels simultaneously demonstrated both negative and positive temperature-responsive swelling behavior. The swelling ratio changed considerably according to swelling temperature. Both DEAEMA and HEMA monomers in terpolymer structure were dominant in temperature-sensitive swelling. Mechanical tests in compression of both as-prepared and swollen-state demonstrated that strength and modulus of hybrid cryogels significantly increased with addition of HNTs without significant loss of mechanical strength. Ultimately, the results of the current system can benefit characterization with analysis tools for the application of innovative materials.


2012 ◽  
Vol 465 ◽  
pp. 141-145
Author(s):  
Hai Yan Wang ◽  
Qian Liao ◽  
Qiao Lan Shao ◽  
Gao Qiu ◽  
Xi Hua Lu

There have much study about thermo-responsive nanogels,which exhibit temperature-controlled volume phase transitions.There have been few reports,however,of electrostatically neutral,thermosensitive nanogels with a high composition of hydrophilic monomer.Here,we describe the synthesis and characterization of a new class of nonionic copolymer nanogels based on N-ispropylacrylamide(NIPAM) and N,N-dimethylacrylamide(DMA),wich exhibit tunable volume phase transition temperatures.And increasing percentages of DMA in copolymer gels raises the LCST,and attenuates and broadens the volume phases transition.Through DLS, AFM and UV-Vis measurement it's size,shape and VPTTs.The character of nonionic NIPAM/DMA nanogels show it's tunable phase transitions promise to be useful for applicatipns in biotechnology and medicine.


2018 ◽  
Vol 72 (3) ◽  
pp. 167-176
Author(s):  
Pero Sailovic ◽  
Branka Rodic-Grabovac ◽  
Snezana Uletilovic

Biologically active fibers as drug carriers have improved characteristics in comparison with conventional medical therapies. Cellulose as a hydrophilic and biocompatible, nontoxic and eco-friendly material, makes a good polymer matrix for obtaining biologically active fibers. Loading drugs on the fiber carrier is accomplished through hydrophobic interactions, which is a prevailing mechanism of drug bonding. These interactions can be achieved by hydrophobic parts of the drug and the fiber carrier or by hydrophobic drugs themselves bonded on the fiber. In this paper, oxidized cellulose (OC) with 0.547, 1.163 and 2.199 mmol/g COOH is produced by using selective oxidation of a cellulose-based bandage. Oxidation has been carried out in mixture of HNO3/H3PO4 2:1 and 1.43 % NaNO2 for 5, 10 and 20 h at 25 ? 1 ?C. The OC sample with 2.199 mmol/g COOH showed the lowest sorption capacity as well as weak mechanical properties, so that the sorption experiments were not further pursued. The other two samples of oxidized cellulose with 0.547 and 1.163 mmol/g COOH have been used for chemical bonding of an analgesic, diclofenac, a derivative of potassium salt. Diclofenac in its structure contains two benzene rings which are linked via a secondary amine. The analgesic also contains a carboxyl group, as well as 2 chlorine atoms. As a result of the presence of these functional groups and structures, diclofenac can build multiple chemical bonds with an oxidized cellulose bandage. The chemical bonding of the drug has been performed using three analgesic solutions with concentrations of c = 2.5?10-3, 3.4?10-3 and 5.1?10-3 mol/L, at the temperature of 26 ? 1oC while desorption was performed in physiological saline solution. The amounts of bonded and released antibiotic were determined by UV-VIS spectroscopy at the wavelength of ?max=276 nm. The maximum amount of bonded drug (0.814 mmol/g OC) has been obtained by sorption from the solution of concentration c=5.1?10-3, while the highest amount of desorbed diclofenac was 0.063 mmol/g OC. The sorption kinetics has been succesfully described by the pseudo-second order model. It was established that the drug bonding was achieved by hydrogen bonds of the drug functional groups with the oxidised cellulose bandage. Low diclofenac relase from the oxsidiesed cellulose (12.5 % in 24 h) is a consequence of formation of multiple bond as well as drug aggregates on fiber surfaces.


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