\”Advanced Materials\”: 3D printing technology quietly reached foaming material

The polymer foam material is widely used in the production life, it is a large and important class of porous material. Currently polymer foams prepared using the blowing agent is mainly used to direct expansion in the resin foam, like making bread, flour, yeast and mixed first knead the dough, CO2 produced by yeast is expanded so that solid under the action of heat fluffy dough into a body. However, this process is inevitable and it is difficult to control the structure and morphology of the cell nucleus, were combined, and other factors will rupture the cells have a greater damage, thereby affecting the performance, how to precisely control the micro-shaped cells appearance and macro-foam structure is still a difficulty. Computer programs incorporating auxiliary additive manufacturing technology (3D printing) obtained in recent years, rapid development, compared to conventional molding technique, which can be the biggest advantage of a precise and rapid prototyping to small micro and nano-size three-dimensional structure of the complex. In order to solve prepare direct expansion foaming process some of the problems existing in the process of polymer foam, from Dr. Harvard University Claas Willem Visser (corresponding author) and Professor Jennifer A. Lewis (co-author) and other researchers 3D printing technology applied to the preparation of polymer foam, the polymer can be first developed a direct-write (polyethylene glycol diacrylate) bubble \”ink\”, by direct writing – preparation of a UV curing manner microscopic cell combination morphology, distribution, and macro adjustable precision foam polymer foam structure, and by changing the composition of the bubble \”ink\”, may also confer new functionality foam. to the research entitled \”Architected Polymer Foams viaDirect Bubble Writing\” is published in \” AdvancedMaterials \” on (see the text description link). Single microscopic bubbles

Preparation of Foam Method directly writing principle

To direct writing \”ink\” for the formation of macro bubbles, as shown in FIG. 1, the inner and outer two-layer structure design researchers special nozzle: inner tube transporting polymer comprising monomer, initiator and polymer precursor solution of a surfactant, the outer tube conveying gas, a mixture of both the nozzle orifice, the bubbles formed can be written \”ink\” from a single bubble drip nozzleDeposited onto a substrate, the ultraviolet polymerization initiator, the adhesive is formed between the macro block of foam bubbles. Wherein, \”ink\” and a gas flow rate of dropping pressure is a key different microscopic morphology of the foam cells was prepared: The theoretical and experimental results, the precursor of the liquid flow rate is plotted with respect to FIG influence of bubbles and pressure \”ink\” form pairs, in a subsequent study, the selected liquid flow rate Q = 10 mL min-1 at a constant rate, the liquid component of the study, pressure and composition of gas, the nozzle parameters such as rate of movement of the foam microstructure and macrostructure.

《先进材料》:3D打印技术悄悄地杀入发泡材料
FIG. 1.A) and curing the foam writing apparatus, the white arrows bubble \”ink\” nozzle outlet, the transparent tube is a gas delivery tube, the tube is white liquid delivery tube, the tube 4 is an ultraviolet gold source; b) preparing a foam schematic; c, d, e) diagram and a schematic view of the nozzle look and enlarged section; f, g) outside the nozzle and the inner hole images; h – k) gas precursor liquid different pressures mix inside the nozzle after discharging bubbles form, the pressure rises successively from left to right; L) and the flow rate of the precursor gas pressure on the liquid bubble \”ink\” shape of the phase diagram; m) written directly prepared by block foam; n, o) different microscope FIG foam pore morphology under magnification.

Compared with the conventional method for preparing foams, has the following four advantages of direct writing method:

One advantage: the cell morphology and controlled distribution

most of the foam is directly related to the performance of the cell morphology, cell morphology precise formulation of the foam and thus excellent properties is prepared directly write the maximum foaming process innovation. Cell morphology including open / closed cell structure, and pore size distribution of these three elements. On the kind of gas is controlled by opening closed-cell structure: that the contact surface of O2 to O2 during polymerization inhibitor having a function as a gas, a monomer depth within the range from about 40um to stop or retard polymerization, thereby thinned cell walls, finally becomes open-cell foam; when N2 is an inert gas source, the polymerization occurs normally, thicker cell walls, closed cell foam. Pore ​​size and distribution by adjusting the gas pressure, a lower pressure will produce monodisperse (2 ≤ P ≤2.7 kPa) bubble \”ink\”, the cell diameter is obtained substantially 0.5 mm, a very uniform distribution; When the pressure increases, bubble into a double dispersion (2.8 ≤P ≤ 3.4 kPa) or even three dispersion (P> 3.6 kPa), to give foam hole diameter is between 0.3 – between 0.7 mm, the distribution is wide.

《先进材料》:3D打印技术悄悄地杀入发泡材料
FIG. 2. a) and b) are open and closed cell foam preparation procedure and X tomography images; c) the foam density and pressure relationship diagram; d, e) monodispersed and bis cell structure and dispersion f) the statistical distribution of the results thereof an aperture; Effect g) gas pressure on the cell aperture. The multilayer structure was prepared multi-layered structure of the foam

changes the nozzle while the nozzle writing spatial position and size of pressure, can be prepared in different 3D frame:

Two advantages materials, such as triangular lattice of FIG. By increasing the gas pressure or slowing the nozzle moving speed, a single grid member will be wider, and vice versa.

《先进材料》:3D打印技术悄悄地杀入发泡材料
FIG 3.a) from left to right are P = 2.4 kPa when the moving speed of the nozzle 35, 70, the line width after writing 150 cured 250 mm s-1 and Condition; B Effect) writing pressure and rate of movement of the nozzle line width; c – f) construction of multilevel triangular lattice macro and micro structure photograph.

Three advantages: gradient structure prepared from a gradient foam mechanical properties

In a continuous process of writing intermittent adjusting the process parameters to change the density of the foam between the local and modulus and other parameters, so that the resulting foam exhibits a gradient of several orders of magnitude the overall mechanical properties, achieved as the accumulation of wood, like a number of different sub-group structural member combined into a large macroscopic. This foam structure is difficult to obtain by conventional foaming methods.

《先进材料》:3D打印技术悄悄地杀入发泡材料
FIG. 4. d) Preparation of a hemispherical structure and composition gradient schematic structural foam; shape change process e) compressive gradient structure; stress with deformation process f) compression, (i ) – (iv) the structure – (iv), respectively corresponding to the region e), (i).

Three advantages: Synthesis of functional Foam

changing the composition of the precursor solution, Such as adding a certain function of the substance, after the foam forming the material can impart new functions to retain the foam. For example, the precursor of the advance was added AgNO3 on, transition post-cured flexible foam containing nanosilver, compression resistance becomes small, and there is a good linear relationship and has a high sensitivity to pressure, the pressure is expected to sensor.

《先进材料》:3D打印技术悄悄地杀入发泡材料
FIG. 5. a) Ag nano bubble image; b) a schematic view of a compression resistance test; C resistance foam prepared under different pressure change with pressure); d) the foam produced at different pressures sensitivity variation with pressure.

summed

The results show the direct write process can be accurately controlled microscopic morphology and macroscopic cell foam structure, the mechanical properties of the foam are then programmed control, and it can also be easily given foam new features to improve future mode of preparation of the foam has a positive role in promoting. The full text link: https: //onlinelibrary.wiley.xilesou.top/doi/10.1002/adma.201904668

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