Rheology of 3D printable ceramic suspensions: effects of non-adsorbing polymer on discontinuous shear thickening

Research on rice starch gel preparation and crosslink network structure-rheological property based on direct-writing 3D printing

Amylopectin and amylose components are natural polymers within rice starch granules, intertwined in specific conditions to form gel polymerized with pore crosslink network, has potential printing properties. In this study, a rice starch gel preparation scheme is proposed for stable properties, and starch granule phase transition mechanism is analyzed based on RVA test during preparation, it can be divided into four-stage, swelling, reacting, homogenizing and self-assembling stages. Gel surface tension and contact angle tested with starch concentration effect, a correlation is developed, reflecting a competition result to gel droplet macro-morphology between the intermolecular cohesion and crosslink network. SEM is used to reveal typical crosslink structures of different starch molecular component proportions, providing objective support for starch gel rheologic property change. Results indicate gel interior crosslink network formed under concentration 12 %, the gel with amylose 4.475 % presents better printing accuracy. Gel shear modulus positively correlated with amylose proportion. Japonica gel under 20 % is of higher viscosity and rapid reassembly ability after interior crosslink network is broken. Max dynamic viscosity is positively correlated with starch concentration. The study aims to provide theoretical and practical support for in-depth analysis of rice starch material application in direct-write 3D printing.

Water-Based Additive-Free Chromic Inks for Printing of Flexible Photochromics and Electrochromics

Digital inkjet printing has become one of the most convenient and efficient technologies for coating chromic materials on flexible substrates with complicated patterns. However, the development of water-based, additive-free chromic inks for inkjet printing still remains a challenge. Herein, three ammonium-functionalized colorless viologen derivatives AV, APV, and AQV with excellent water solubilities are utilized as chromes in the chromic inks due to their excellent photochromic and electrochromic properties. Water, ethanol, and ethylene glycol are selected as cosolvents, and their contents in this ternary solvent system have been optimized to achieve comprehensive rheological properties. With the H2O:EtOH:EG weight ratio of 8:1:7, the chromic ink based on AV realizes a viscosity of 4.69 mPa·s, a surface tension of 45.13 mN/m, and a Z value of 3.87. Without adding any additive, the as-prepared chromic inks can be printed on flexible substrates, such as paper and poly(ethylene terephthalate) (PET) films, by a conventional inkjet printer with inherent high resolutions. The printed patterns are initially invisible due to the colorless characteristics of the chromic inks. Interestingly, the printed films are responsive to both light and electric stimuli. Upon irradiation by UV light, a series of sentences with font sizes from 5 to 12 points and four quick response codes with different lattice resolutions clearly appear on the printed paper. Meanwhile, after printing on an indium tin oxide-coated PET substrate, electrochromic devices (ECDs) can be facilely fabricated by covering a hydrogel electrolyte on the printed films. Upon application of different potentials, the assembled ECDs exhibit "Peking Opera facial makeup" patterns with different colors. Therefore, the developed water-based additive-free chromic inks can be utilized for information display and encryption applications.