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Related Concept Videos

Solubility03:00

Solubility

Solution, Solubility, and Solubility Equilibrium
A solution is a homogeneous mixture composed of a solvent, the major component, and a solute, the minor component. The physical state of a solution—solid, liquid, or gas—is typically the same as that of the solvent. Solute concentrations are often described with qualitative terms such as dilute (of relatively low concentration) and concentrated (of relatively high concentration).
In a solution, the solute particles (molecules, atoms, and/or ions)...
Recrystallization: Solid–Solution Equilibria01:10

Recrystallization: Solid–Solution Equilibria

Recrystallization is a purification technique used to separate impurities from solid compounds. In this technique, no chemical reactions occur. Instead, it exploits physical properties only, specifically, the solubility differences between the desired compound and impurities, either at a single temperature or at different temperatures, and under other selected conditions. The solid-solution equilibrium (solubility equilibrium) of each component in the solution represents a binary phase...
Factors Affecting Dissolution: Polymorphism, Amorphism and Pseudopolymorphism01:21

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Polymorphism refers to the existence of a drug substance in multiple crystalline forms, known as polymorphs. Recently, this term has been expanded to include solvates (forms containing a solvent), amorphous forms (non-crystalline forms), and desolvated solvates (forms from which the solvent has been removed).
Some polymorphic crystals possess lower aqueous solubility than their amorphous counterparts, leading to incomplete absorption. For instance, the oral suspension of Chloramphenicol, which...
Solubility Equilibria: Overview01:09

Solubility Equilibria: Overview

When a substance such as sodium chloride is added to water, it dissolves, forming an aqueous solution. The extent of dissolution is called solubility. The process of dissolution can exist in equilibrium, just like other chemical processes. Solubility equilibria are also called precipitation equilibria because the process of solubility can be reversible. The reverse of the solubility process is called precipitation.
Solubility is important in biological and environmental processes. A notable...
Enthalpy of Solution02:39

Enthalpy of Solution

There are two criteria that favor, but do not guarantee, the spontaneous formation of a solution:
Energetics of Solution Formation02:35

Energetics of Solution Formation

The formation of a solution is an example of a spontaneous process, which is a process that occurs under specified conditions without energy from some external source.
When the strengths of the intermolecular forces of attraction between solute and solvent species in a solution are no different than those present in the separated components, the solution is formed with no accompanying energy change. Formation of the solution requires the solute–solute and solvent–solvent electrostatic forces to...

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Fabricating Degradable Thermoresponsive Hydrogels on Multiple Length Scales via Reactive Extrusion, Microfluidics, Self-assembly, and Electrospinning
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Reversible changes in solution pH resulting from changes in thermoresponsive polymer solubility.

Yanfei Yang1, Alexander J Mijalis, Hui Fu

  • 1Department of Chemistry, Texas A&M University, College Station, Texas 77842-3012, USA.

Journal of the American Chemical Society
|April 12, 2012
PubMed
Summary

Polymers with lower-critical solution temperature (LCST) properties can alter solution pH. This pH change occurs reversibly when amphoteric pendant groups on the polymer interact with changing hydration during phase transitions.

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Area of Science:

  • Polymer Chemistry
  • Physical Chemistry
  • Solution Chemistry

Background:

  • Polymers with lower-critical solution temperature (LCST) exhibit a phase transition from soluble to insoluble with increasing temperature.
  • Amphoteric pendant groups on polymers, such as carboxylate or ammonium salts, experience altered solvation environments during LCST-induced phase separation.
  • Changes in solvation significantly impact the acidity or basicity of these amphoteric groups.

Purpose of the Study:

  • To investigate the reversible changes in solution pH induced by the lower-critical solution temperature (LCST) phenomenon in polymers.
  • To explore the influence of amphoteric pendant groups on polymer behavior during phase transitions.
  • To demonstrate the potential for controlling bulk solution pH through polymer LCST events.

Main Methods:

  • Utilizing polymers with pendant amphoteric groups (carboxylate salts, ammonium salts) and lower-critical solution temperature (LCST) properties.
  • Dissolving polymers in solutions with pH near the pK(a) of the pendant groups.
  • Monitoring solution pH changes as a function of temperature during LCST events.
  • Observing pH changes using common indicators and direct pH measurements.
  • Investigating the effect of kosmotropic salts on LCST-induced pH changes.

Main Results:

  • LCST-induced polymer precipitation leads to significant and reversible changes in the acidity/basicity of amphoteric pendant groups.
  • Carboxylate salts capture protons, forming carboxylic acids, while ammonium salts release protons, forming neutral amines during phase separation.
  • Polymers like poly(N-isopropylacrylamide) with sufficient comonomer loading can alter the bulk solution pH near their LCST.
  • Reversible pH shifts were visually confirmed with indicators and quantitatively measured via pH monitoring.
  • Addition of kosmotropic salts also triggers reversible solution pH changes associated with LCST events.

Conclusions:

  • The hydration changes accompanying polymer LCST events can be harnessed to modulate the acidity/basicity of pendant amphoteric groups.
  • This phenomenon allows for reversible control over the bulk solution pH by tuning polymer structure and environmental conditions.
  • The study demonstrates a novel method for pH manipulation using stimuli-responsive polymers.