Photopatterning polymerization inhibition volumes by two-color irradiation enables exceptional 3D printing speed and functionality.

A simple low-cost experiment has been developed for the measurement of the binary diffusion coefficients of liquid substances. The experiment is suitable for demonstrating molecular diffusion to small or large undergraduate classes in chemistry or chemical engineering. Students use a cell phone camera in conjunction with open-source image processing software to measure concentrations of a colored species in a clear liquid, as a function of position and time. Three fundamental principles in mass transfer and spectrophotometry are demonstrated: Fick's first and second laws of diffusion and the Beer-Lambert law for absorption of light. The measured value for the binary diffusion coefficient for potassium permanganate in water using this method was found to be within 10% of literature values at the 95% confidence interval. M olecular diffusion is a core component of the syllabus for the teaching of undergraduate chemistry, physics, and chemical engineering. It has been reported that students find this particular concept difficult to grasp, 1−3 and therefore, practical demonstrations of the phenomenon are valuable teaching aids. This article describes a simple, low-cost experimental technique which enables students to measure binary diffusion coefficients (D AB ) of a colored species dissolved in a clear liquid.Many studies have shown that students find molecular diffusion difficult to conceptualise, even at third-and fourth-year undergraduate level. Westbrook and Marek 1 showed that, despite advanced instruction, undergraduate-level science students had no better understanding of diffusion than seventh-grade life science students. In an investigation into the effect of simulated experiments, Meir et al. 2 identified the following specific misconceptions and lack of knowledge:• the concept of concentration • the relationship between an amount of substance and its concentration • kinetic energy and random molecular motion of a species • species supposedly having a directional motion toward regions of lower concentration of that species • equilibrium and the effect on diffusion rates as equilibrium is approached Marek et al. 3 showed convincingly that students who underwent a laboratory-based interactive learning cycle showed a 94% improvement in understanding. Students who attended expository teaching activities (such as lectures and discussions) showed only a 58% improvement in understanding. Similarly, Meir et al. 2 demonstrated improved understanding after students performed simulated experiments on a computer. These studies highlight the effectiveness of practical activities in the learning of diffusion concepts.Many experimental methods for the study of diffusion have been reported, all of which use costly apparatus, and/or require knowledge of various physical properties of the species which are not readily available. Kraus and Tye 4 used a backlit capillary tube and cathetometer telescope, having first measured the refractive characteristics of the apparatus and the solvent. Nishijima and Oster 5 developed an op...

a desired 3D part. Typically, stereolithography produces parts in discrete layers. Exposed areas are cured through the full layer height, whereupon the part is repositioned and recoated with resin before the next layer is exposed. Recently, continuous stereolithographic technologies have been developed which increase print speeds by eliminating the time-consuming repositioning and recoating steps. [19,20] Print speed in continuous stereolithography is dependent on the resin absorbance height, with low-absorbance resins allowing extremely high print speeds of up to 2000 mm h −1 at the cost of part fidelity. [20] In stereolithography, the penetration depth of light in the resin limits accuracy along the vertical axis: unaccounted-for light propagation can cause undesired curing, known as cure-through, overcure, [21,22] the back-side effect, [23] or printthrough error. [19,24] This phenomenon can also contribute to cross-linking heterogeneity, introducing internal stresses which can deform the part and further reduce fidelity. [25] The prevalent strategy to mitigate cure-through is to add nonreactive light absorbers to the resin formulation. [21,[25][26][27][28] Highly absorbing resins have been widely adopted despite the slower print speeds needed to ensure fully cured layers. Alternatively, cure-through can be mitigated without sacrificing speed by modifying the projected images, known as slices, based on modeling of the curing process. Optimization-based methods to eliminate cure-through by adjusting model dimensions have been developed for external surfaces and internal voids in traditional stereolithography. [22,24,29] Manual adjustments to account for cure-through have also been reported. [30] Nevertheless, slice correction has not been described for continuous stereolithography, where cure-through is a more significant and complex problem. Furthermore, existing models of continuous stereolithography are not tailored to this application. [31][32][33] Here, we present a curing model and a slice correction algorithm for continuous stereolithography. Previous noncontinuous approaches used iterative and heuristic processes to find optimal corrections and were restricted to black and white pixels; our correction method uses grayscale, which has previously only been used to improve lateral resolution, [34] along with an exact mathematical solution to precisely set the dose profile within a part. We also present experimental validation of our model and correction approach using a recently developed two-color continuous stereolithographic 3D printer. [20] These methods are Continuous stereolithography offers significant speed improvements over traditional layer-by-layer approaches but is more susceptible to cure-through, undesired curing along the axis of exposure. Typically, cure-through is mitigated at the cost of print speed by reducing penetration depth in the photopolymer resin via the addition of nonreactive light absorbers. Here, a mathematical approach is presented to model the dose profile in a part produced ...

A unique glass etching process creates variable height channels capable of separating particles or cells by size or deformability.

Volumetric additive manufacturing (VAM) enables rapid printing into a wide range of materials, offering significant advantages over other printing technologies, with a lack of inherent layering of particular note. However, VAM suffers from striations, similar in appearance to layers, and similarly limiting applications due to mechanical and refractive index inhomogeneity, surface roughness, etc. We hypothesize that these striations are caused by a self-written waveguide effect, driven by the gelation material nonlinearity upon which VAM relies, and that they are not a direct recording of non-uniform patterning beams. We demonstrate a simple and effective method of mitigating striations via a uniform optical exposure added to the end of any VAM printing process. We show this step to additionally shorten the period from initial gelation to print completion, mitigating the problem of partially gelled parts sinking before print completion, and expanding the range of resins printable in any VAM printer.