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Inkjet-based three-dimensional (3D) printing is widely used for fast and efficient non-contact manufacturing, yet it suffers from several drawbacks, such as coarse resolution, lack of adhesion, manufacturing inconsistency, and uncertain final part mechanical properties. These undesirable effects are related to complex flow phenomena in colloidal droplets in inkjet 3D printing, particularly the internal flows and droplet deformations during the deposition and drying processes. These challenges are due to the colloidal suspension droplets being kept in the liquid state during printing. To overcome these disadvantages, this paper presents a novel freezing-sublimation-based inkjet 3D printing concept that freezes the colloidal droplets upon impact followed by sublimation, eliminating the undesirable particle transport and fluid motions during deposition. A series of experiments were conducted to characterize the colloidal droplet behaviors during the impinging/freezing and sublimation processes and evaluate the effects of the freezing process on droplet impinging dynamics as well as the final deposition patterns through sublimation. It was demonstrated that the deposition patterns obtained from this new method are much more uniform than the conventional evaporation-based deposition method. Both qualitative and quantitative methods were applied to analyze the colloidal droplet profiles during the printing process (impinging, freezing, and sublimation), as well as the final deposition patterns. The study shows promising results of using this new method, providing a foundation for the development of the novel freezing-sublimation-based inkjet 3D printing technique. 

Abstract In this paper, an experimental study was conducted to characterize the dynamics and thermal evolutions of colloidal droplets impinging and freezing on solid surfaces with different wettabilities (i.e., superhydrophobic vs. hydrophilic) towards the development of a novel freezing-based inkjet additive manufacturing (AM) technology. The experiments were carried out in the Freeze Layering Inkjet Printing (FLIP) facility in the Mechanical Engineering Department of the City College of New York (CCNY). While the transient impinging/freezing dynamics of colloidal droplets were resolved by using a high-speed imaging system, the thermal evolutions of the freezing colloidal droplets were also characterized by using a high-speed high-resolution Infrared (IR) thermal imaging system. In addition, the deposition patterns formed under the conventional evaporation-based approach and the novel freezing-sublimation approach were also evaluated by using an automated high-accuracy freeze dryer facility. It was found that the time scale of the dynamic process (i.e., impact, spreading, receding, rebounding, and settling) was much faster than the thermal process (i.e., nucleation and solidification) for both surfaces. The dynamics of the colloidal droplets during the impinging process were coupled with the thermal processes that govern the freezing of the droplets. The surface wettability had a direct effect on both the freezing footprint and the freezing rate. 

Morphing structures are often engineered with stresses introduced into a flat sheet by leveraging structural anisotropy or compositional heterogeneity. Here, we identify a simple and universal diffusion-based mechanism to enable a transient morphing effect in structures with parametric surface grooves, which can be realized with a single material and fabricated using low-cost manufacturing methods (e.g., stamping, molding, and casting). We demonstrate from quantitative experiments and multiphysics simulations that parametric surface grooving can induce temporary asynchronous swelling or deswelling and can transform flat objects into designed, three-dimensional shapes. By tuning the grooving pattern, we can achieve both zero (e.g., helices) and nonzero (e.g., saddles) Gaussian curvature geometries. This mechanism allows us to demonstrate approaches that could improve the efficiency of certain food manufacturing processes and facilitate the sustainable packaging of food, for instance, by creating morphing pasta that can be flat-packed to reduce the air space in the packaging. 

Despite global commitments and efforts, a gender‐based division of paid and unpaid work persists. To identify how psychological factors, national policies, and the broader sociocultural context contribute to this inequality, we assessed parental‐leave intentions in young adults (18–30 years old) planning to have children (N = 13,942; 8,880 identified as women; 5,062 identified as men) across 37 countries that varied in parental‐leave policies and societal gender equality. In all countries, women intended to take longer leave than men. National parental‐leave policies and women's political representation partially explained cross‐national variations in the gender gap. Gender gaps in leave intentions were paradoxically larger in countries with more gender‐egalitarian parental‐leave policies (i.e., longer leave available to both fathers and mothers). Interestingly, this cross‐national variation in the gender gap was driven by cross‐national variations in women's (rather than men's) leave intentions. Financially generous leave and gender‐egalitarian policies (linked to men's higher uptake in prior research) were not associated with leave intentions in men. Rather, men's leave intentions were related to their individual gender attitudes. Leave intentions were inversely related to career ambitions. The potential for existing policies to foster gender equality in paid and unpaid work is discussed.