Aqueous Particle Dispersion Homogeneous Drying Pattern
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Solution Overview
Problem
The coffee ring effect, characterized by the formation of circular stains during the drying of aqueous particle dispersions, poses challenges in achieving uniform deposition in technologies like coating techniques and inkjet printing, as existing strategies require customized substrates, surfactants, or particles, limiting their versatility.
Innovation Solution
An aqueous particle dispersion with modified particles, comprising a solid core and a polymeric shell of a water-soluble interfacially-active polymer with a molecular weight over 10 kDa, is developed, which exhibits a homogeneous drying pattern by adjusting the surface tension to 60-72 mN/m, independent of particle shape, allowing for uniform particle film formation and suppression of the coffee ring effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional strategies (soluble polymers, surfactants, customized particles) are used to suppress the coffee ring effect, then uniform drying pattern is achieved, but system complexity and customization requirements increase
Solution Approach 1:
The invention changes the surface tension parameter of the aqueous particle dispersion to a specific range (60-72 mN/m) by adding water-soluble interfacially-active polymers. This parameter change suppresses the coffee ring effect and achieves uniform drying patterns without requiring customized substrates or complex surfactant systems. The polymer concentration is adjusted to achieve the target surface tension range, providing a simple and versatile solution.
Solution Approach 2:
The water-soluble interfacially-active polymer acts as an intermediary substance that mediates between the particle suspension and the drying process. By adding this polymer, the surface tension is modified to prevent capillary flow-driven particle transport to the droplet edge, thereby suppressing the coffee ring effect without requiring customization of the substrate or particle morphology.
2Manufacturing precision
If particle aggregation or electrostatic adsorption is induced to suppress coffee ring effect, then uniform deposition is achieved, but control precision and system tailoring requirements increase
Solution Approach 1:
Instead of precisely controlling particle-particle and particle-interface interactions through aggregation or electrostatic adsorption, the invention changes the surface tension parameter of the bulk dispersion. This macroscopic parameter change simplifies the system by avoiding the need for precise control of microscopic interaction forces, while still achieving uniform particle deposition.
3Manufacturing precision
If ellipsoidal particles are used to achieve uniform drying behavior, then coffee ring effect is suppressed, but manufacturing versatility is reduced
Solution Approach 1:
The invention provides a universal solution by modifying the surface tension of the dispersion medium rather than relying on specific particle morphology. The water-soluble interfacially-active polymer can be applied to various particle materials and shapes, making the method versatile and broadly applicable without requiring customized particle designs.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The approach results in a uniform particle film coverage over the entire substrate surface, effectively preventing convective transport of particles to the droplet edge during drying, thus overcoming the coffee ring effect for various commercial particles and applications.
Implementation Method 1
the polymeric shell comprises, or consists of, a monolayer of a water-soluble interfacially-active polymer having a molecular weight of more than 10 kDa, which is adsorbed to the solid core particle
Implementation Method 2
The capillary flow can be reduced by an increase in viscosity due to the addition of soluble polymers or by invoking Maragoni flows to at least partially counteract the capillary flow
Implementation Method 3
wherein the surface tension of the dispersion is in a range of from 60 to 72 mN/m, preferably from 65 to 72 mN/m and more preferably from 67 to 72 mN/m
Implementation Method 4
by invoking Maragoni flows (Hu, H. et al.; J. Phys. Chem. B, 110, 7090-7094 (2006)) to at least partially counteract the capillary flow
Data Source
Figure 1~2c
Figure 3a~4d
Figure 5a~5i
AI summary
The present invention relates to a process for producing an aqueous particle dispersion comprising the steps of: a) providing a dispersion consisting of water and solid core particles, b) providing an aqueous solution of a water-soluble, interfacially-active polymer having a molecular weight of more than 10 kDa, c) mixing said aqueous dispersion of solid core particles with said aqueous polymer solution, d) removing free polymer from the obtained mixture; wherein, in step c), the amount of the water-soluble, interfacially-active polymer mixed with said aqueous dispersion of solid core particles exceeds the amount of polymer required to coat the surface of each of the solid core particles with a monolayer of the polymer, and wherein step d) is repeated until the surface tension of the resulting modified particle dispersion is in a range of from 60 to 72 mN/m, preferably from 65 to 72 mN/m and more preferably from 67 to 72 mN/m. The present invention also relates to an aqueous particle dispersion exhibiting a homogenous drying pattern as well as a film made thereof and the use of the aqueous particle dispersion.