scholarly journals Fabrication of alginate/chitosan complex fibers via diffusion controlled in-situ polyelectrolyte complexation

2021 ◽  
Vol 2 ◽  
pp. 100030
Author(s):  
Wentao Huang ◽  
Liping Zhu ◽  
Dezhong Liu ◽  
Jiefu Li ◽  
Shuguang Yang
Keyword(s):  
Diffusion Controlled ◽  
Polyelectrolyte Complexation

scholarly journals Production and Characterization of Chitosan–Polyanion Nanoparticles by Polyelectrolyte Complexation Assisted by High-Intensity Sonication for the Modified Release of Methotrexate

2020 ◽  
Vol 13 (1) ◽  
pp. 11 ◽  
Author(s):  
Yhors Ciro ◽  
John Rojas ◽  
Maria Alhajj ◽  
Gustavo Carabali ◽  
Constain Salamanca
Keyword(s):  
Zeta Potential ◽  
Maleic Acid ◽  
High Intensity ◽  
Physical Stability ◽  
Release Mechanism ◽  
Diffusion Controlled ◽  
Polyelectrolyte Complexation ◽  
Anticancer Treatment ◽  
Particle Parameters

A promising strategy to improve the effectivity of anticancer treatment and decrease its side effects is to modulate drug release by using nanoparticulates (NPs) as carriers. In this study, methotrexate-loaded chitosan–polyanion nanoparticles were produced by polyelectrolyte complexation assisted by high-intensity sonication, using several anionic polymers, such as the sodium and potassium salts of poly(maleic acid-alt-ethylene) and poly(maleic acid-alt-octadecene), here named PAM-2 and PAM-18, respectively. Such NPs were analyzed and characterized according to particle size, polydispersity index, zeta potential and encapsulation efficiency. Likewise, their physical stability was tested at 4 °C and 40 °C in order to evaluate any change in the previously mentioned particle parameters. The in vitro methotrexate release was assessed at a pH of 7.4, which simulated physiological conditions, and the data were fitted to the heuristic models of order one, Higuchi, Peppas–Sahlin and Korsmeyer–Peppas. The results revealed that most of the MTX-chitosan–polyanion NPs have positive zeta potential values, sizes <280 nm and monodisperse populations, except for the NPs formed with PAM-18 polyanions. Further, the NPs showed adequate physical stability, preventing NP–NP aggregation. Likewise, these carriers modified the MTX release by an anomalous mechanism, where the NPs formed with PAM-2 polymer led to a release mechanism controlled by diffusion and relaxation, whereas the NPs formed with PAM-18 led to a mainly diffusion-controlled release mechanism.

In-Situ, Time Resolved, Kinetics of Reactions in Co-Ge thin Films

1991 ◽  
Vol 237 ◽  
Author(s):  
R. M. Walser ◽  
Byung-Hak Lee ◽  
Alaka Valanju ◽  
Winston Win ◽  
M. F. Becker
Keyword(s):  
Depth Profiling ◽  
Laser Interferometry ◽  
Semiconductor Interface ◽  
Time Resolved ◽  
Interface Reactions ◽  
Valuable Adjunct ◽  
Diffusion Controlled ◽  
Sputter Deposited ◽  
Time Required

ABSTRACTWe report the first kinetic study of metal-semiconductor interface reactions using in-situ, time resolved, laser interferometry. Diffusion couples with Co/Ge thicknesses of 1500 Å/1500 Å were sputter deposited on silicon wafers, and vacuum-annealed at temperatures between 300°C-400°C. Under these conditions polycrystalline CoGe was expected to form [1]. Real time laser (HeNe 6328 Å) interferograms for each anneal were recorded in-situ. These data were supplemented by information from AES and X-ray.For temperatures below 400°C the diffusion controlled formation of CoGe was observed. The composition was confirmed by Auger depth profiling that showed uniform Co and Ge concentrations when the reaction went to completion. The well defined interferences fringes were formed by the dissolution of amorphous Ge. The activation energy = 1.6 eV for the formation of CoGe were determined with precision from the temperature dependence of the time required to anneal the fixed λ/4 distance between adjacent minima and maxima of the interferogram. We discuss the evidence for formation of an intermediate Co-rich compound following the initial diffusion of Co into Ge. The results of these experiments indicate that optical interferometry will be a valuable adjunct to other techniques used to study metal-semiconductor interface reactions.

scholarly journals Tetrathiafulvalene: A Gate to the Mechanochemical Mechanisms of Electron Transfer Reactions

Crystals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 482
Author(s):  
Richard Chen ◽  
Mehmet Kerem Gokus ◽  
Silvina Pagola
Keyword(s):  
Mechanochemical Synthesis ◽  
Amorphous Material ◽  
In Situ Monitoring ◽  
Ex Situ ◽  
Mechanochemical Reaction ◽  
Charge Transfer Complexes ◽  
Spectroscopic Techniques ◽  
Diffusion Controlled ◽  
Mechanochemical Reactions

This report describes aspects of our previous studies of the mechanochemical synthesis of charge transfer complexes of the electron donor tetrathiafulvalene, which are relevant to the use of laboratory X-ray powder diffraction for ex situ monitoring of mechanochemical reactions toward investigating their mechanisms. In particular, the reaction of tetrathiafulvalene and chloranil was studied under neat mechanochemical conditions and liquid-assisted grinding with diethyl ether (1 μL/mg). The product in both cases is the green tetrathiafulvalene chloranil polymorph and the mechanism of the redox reaction is presumably the same. However, while the kinetic profile of the neat mechanochemical synthesis was fitted with a second-order rate law, that of the overall faster liquid-assisted grinding reaction was fitted with the Ginstling-Brounshtein 3D diffusion-controlled model. Hence, the diffusional processes and mass transfer bringing the reactants together and separating them from products must be different. Diffraction measurements sensitive to crystalline phases and amorphous material, combined with in situ monitoring by spectroscopic techniques, will ultimately afford a better understanding of mechanochemical reaction mechanisms, a hot topic in mechanochemistry.

Diffusion-Controlled Nanocrystallization of the Fe73.5Cu1Nb3Si15.5B7 Finemet Amorphous Alloy

2008 ◽  
Vol 570 ◽  
pp. 120-125
Author(s):  
R.M. Ribeiro ◽  
R.S. de Biasi ◽  
D.R. dos Santos ◽  
Dílson S. dos Santos
Keyword(s):  
Differential Scanning Calorimetry ◽  
Amorphous Alloy ◽  
Small Angle ◽  
Nucleation And Growth ◽  
Amorphous Metallic Alloy ◽  
Scanning Calorimetry ◽  
X Ray ◽  
X Ray Scattering ◽  
Diffusion Controlled

Crystallization of the amorphous metallic alloy Fe73.5 Cu1Nb3 Si8.5 B14 was investigated by ferromagnetic resonance (FMR), small angle in situ X-ray scattering (SAXS/WAXS) and differential scanning calorimetry (DSC). Only one crystalline phase was observed by WAXS and only one peak was observed by DSC. The activation energies, calculated from FMR and DSC data, were 287 kJ.mol-1 and 313.4 kJ.mol-1, respectively. The values calculated for the Avrami exponent were 0.98 (FMR) and 1.4 (DSC). These values correspond to different mechanisms of nucleation and growth; however, the SAXS /WAXS results suggest that the dominant mechanisms are nucleation and growth of crystals from small dimensions.

Influence of oxygen partial pressure on the kinetics of YBa2Cu3O7−x formation

1994 ◽  
Vol 9 (2) ◽  
pp. 275-285 ◽  
Author(s):  
V. Milonopoulou ◽  
K.M. Forster ◽  
J.P. Formica ◽  
J. Kulik ◽  
J.T. Richardson ◽  
...  
Keyword(s):  
X Ray Diffraction ◽  
Decomposition Products ◽  
Time Resolved ◽  
X Ray ◽  
Formation Kinetics ◽  
Dimensional Diffusion ◽  
Diffusion Controlled ◽  
Gas Atmosphere ◽  
Kinetics Of

The YBa2Cu3O7−x formation kinetics from a spray-roasted precursor powder containing Y2O3, BaCO3, and CuO was followed via in situ, time-resolved x-ray diffraction as a function of gas atmosphere and temperature. In inert atmospheres, BaCO3 and CuO form BaCu2O2 which subsequently reacts with Y2O3 to form YBa2Cu3O6. However, YBa2Cu3O6 decomposes at temperatures exceeding 725 °C with Y2BaCuO5 being one of the decomposition products. In oxidizing atmospheres, YBa2Cu3O7−x formation involves the BaCuO2. At high temperatures (800–840 °C), oxygen increases the yield of YBa2Cu3O6. A nuclei growth model assuming two-dimensional, diffusion-controlled growth with second-order nucleation rate fits the experimental data.

In situ HREM of interface interactions

1993 ◽  
Vol 51 ◽  
pp. 830-831
Author(s):  
Robert Sinclair ◽  
Toyohiko J. Konno
Keyword(s):  
Amorphous Material ◽  
Equilibrium Phase ◽  
High Resolution Electron Microscopy ◽  
Atomic Scale ◽  
Orientation Relationships ◽  
Interface Reactions ◽  
Diffusion Controlled ◽  
Resolution Electron

We have applied in situ high-resolution electron microscopy (HREM) to the study of interface reactions, particularly in metal-semiconductor systems. There is contrasting behavior whether or not the manufactured interface undergoes a chemical reaction. The in situ technique allows determination of the reaction mechanisms on an atomic scale.Reactive interfaces are characterized by systems in which new chemical compounds are formed (e.g., silicides for metal-silicon interfaces, metal gallides and arsenides for GaAs, etc.). We found that the equilibrium phase formation is often preceded by a solid-state amorphization reaction. In situ observations allow very precise measurement of the reaction rate in a sufficient temperature range to confirm that this process is diffusion controlled. Crystallization of the amorphous material can be followed as well as the development of any crystallographic orientation relationships. A ledge growth mechanism can easily be distinguished from a random process.It might be expected that non-reactive interfaces are stable upon heating.

THERMOREVERSIBLE, MUCOADHESIVE IN SITU GELLING FORMULATIONS FOR NASAL DELIVERY OF PROPRANOLOL HYDROCHLORIDE

INDIAN DRUGS ◽  
2013 ◽  
Vol 50 (09) ◽  
pp. 41-51
Author(s):  
R Bhat ◽  
◽  
Z. Abbas ◽  
N.G.N. Swamy
Keyword(s):  
Nasal Delivery ◽  
Propranolol Hydrochloride ◽  
Gelation Temperature ◽  
Enhanced Absorption ◽  
Diffusion Controlled ◽  
Thixotropic Behaviour ◽  
In Situ Gelling ◽  
Carbopol 934P

Mucoadhesive, thermoreversible propranolol hydrochloride formulations were made to overcome firstpass metabolism, to prolong the drug residence time in the nasal cavity and to improve the therapeutic efficacy. In situ gelling formulations were prepared by cold technique using Pluronic F-127, Pluronic F-68 / Polyvinyl Alcohol complex and Carbopol 934P as the mucoadhesive polymer. Formulations were so modulated as to have gelation temperature below 340C to ensure gelation at the physiological temperature after intranasal administration. Gelation was characterized by physical appearance as well as by rheological evaluation. The gelation temperature decreased with increase in Carbopol concentration, whereas mucoadhesive force increased. The formulations displayed a thixotropic behaviour. The pH of the nasal gels was found to be in the range of 5.3 to 5.6 very much ideal for nasal delivery. The results of in vitro drug diffusion studies across the sheep nasal mucosa indicated that the drug release increased with increase in Carbopol concentration. The release was found to be matrix diffusion controlled and occurred by Fickian mechanism. It could be concluded that, the mucoadhesive, in situ gelling formulations of propranolol hydrochloride proved to be physically stable, convenient, effective nasal delivery systems ensuring prolonged nasal residence and assuring enhanced absorption.

Moisture Intrusion in Sio2/Epoxy Interfaces

1989 ◽  
Vol 153 ◽  
Author(s):  
Ken M. Takahashi
Keyword(s):  
Water Adsorption ◽  
Diglycidyl Ether ◽  
Interfacial Bond ◽  
Conduction Path ◽  
Low Frequencies ◽  
Impedance Measurements ◽  
Diethylene Triamine ◽  
Diffusion Controlled ◽  
Property Changes

SummaryIn-situ interfacial impedance measurements were used to study the effects of moisture at 80 °C on the interface between oxidized silicon and a diglycidyl ether of bisphenol A (DGEBA) epoxy cured with diethylene triamine (DETA). Using two electrode configurations, admittances attributable to bulk and interfacial conduction processes were distinguished. Bulk impedance measurements followed Randles behavior; conduction in the bulk epoxy was ionic, and was diffusion controlled at low frequencies. Equivalent circuit models were used to demonstrate that an apparent interfacial conduction process was caused by distributed current leakage into the silicon subphase, not a true interfacial conduction path that would indicate water adsorption or interfacial aggregation. However, transitions in diffusivity and bulk epoxy permittivity behavior above a 70-80% relative humidity threshold were observed. Effective epoxy permittivity (∈c) jumped to values indicative of a water cluster induced Maxwell-Wagner relaxation. The humidity threshold corresponds to a level that has been associated with adhesion loss in epoxies. It appears that epoxy adhesion losses result from bulk epoxy property changes at high humidity rather than interfacial bond displacement or delamination.

scholarly journals Tracking the Diffusion-Controlled Lithiation Reaction of LiMn2O4 by In Situ TEM

2020 ◽  
Vol 3 (6) ◽  
pp. 5405-5414
Author(s):  
Torben Erichsen ◽  
Björn Pfeiffer ◽  
Vladimir Roddatis ◽  
Cynthia A. Volkert
Keyword(s):  
In Situ Tem ◽  
Diffusion Controlled
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