Abstract:Solid transfer technology from mixtures is gaining ever-increasing attention from materials scientists and production engineers due to their high potential in near net-shaped production of cost-effective engineering components. Dip coating, a wet deposition method, is an effective and straightforward way of thin-film/layers formation. The dipping mixtures are often embedded with inorganic fillers, nanoparticles, or clusters (d<30 nm) that produce a thin film ranging from nm to couple microns. An increas… Show more
“…The mixture preparation is shown in Fig. 1 and discussed in detail elsewhere 54 . Figure 1 SEM micrographs of particles added to the homogeneous LCS to make the heterogeneous mixture.…”
Section: Methodsmentioning
confidence: 99%
“…For submicron size particles, the electrostatic force and van der Waals are prominent for adhesion to the substrate due to their large specific surface area. However, for larger particles ( µm), the specific surface area is reduced, which makes them non-interacting and non-agglomerating particles in the liquid matrix or otherwise known as the non-Brownian regime 20 , 53 , 54 . The mechanism of non-Brownian microparticle (avg.…”
Micro-scale inorganic particles (d > 1 µm) have reduced surface area and higher density, making them negatively buoyant in most dip-coating mixtures. Their controlled delivery in hard-to-reach places through entrainment is possible but challenging due to the density mismatch between them and the liquid matrix called liquid carrier system (LCS). In this work, the particle transfer mechanism from the complex density mismatching mixture was investigated. The LCS solution was prepared and optimized using a polymer binder and an evaporating solvent. The inorganic particles were dispersed in the LCS by stirring at the just suspending speed to maintain the pseudo suspension characteristics for the heterogeneous mixture. The effect of solid loading and the binder volume fraction on solid transfer has been reported at room temperature. Two coating regimes are observed (i) heterogeneous coating where particle clusters are formed at a low capillary number and (ii) effective viscous regime, where full coverage can be observed on the substrate. ‘Zero’ particle entrainment was not observed even at a low capillary number of the mixture, which can be attributed to the presence of the binder and hydrodynamic flow of the particles due to the stirring of the mixture. The critical film thickness for particle entrainment is $${h}^{*}=0.16a$$
h
∗
=
0.16
a
for 6.5% binder and $${h}^{*}=0.26a$$
h
∗
=
0.26
a
for 10.5% binder, which are smaller than previously reported in literature. Furthermore, the transferred particle matrices closely follow the analytical expression (modified LLD) of density matching suspension which demonstrate that the density mismatch effect can be neutralized with the stirring energy. The findings of this research will help to understand this high-volume solid transfer technique and develop novel manufacturing processes.
“…The mixture preparation is shown in Fig. 1 and discussed in detail elsewhere 54 . Figure 1 SEM micrographs of particles added to the homogeneous LCS to make the heterogeneous mixture.…”
Section: Methodsmentioning
confidence: 99%
“…For submicron size particles, the electrostatic force and van der Waals are prominent for adhesion to the substrate due to their large specific surface area. However, for larger particles ( µm), the specific surface area is reduced, which makes them non-interacting and non-agglomerating particles in the liquid matrix or otherwise known as the non-Brownian regime 20 , 53 , 54 . The mechanism of non-Brownian microparticle (avg.…”
Micro-scale inorganic particles (d > 1 µm) have reduced surface area and higher density, making them negatively buoyant in most dip-coating mixtures. Their controlled delivery in hard-to-reach places through entrainment is possible but challenging due to the density mismatch between them and the liquid matrix called liquid carrier system (LCS). In this work, the particle transfer mechanism from the complex density mismatching mixture was investigated. The LCS solution was prepared and optimized using a polymer binder and an evaporating solvent. The inorganic particles were dispersed in the LCS by stirring at the just suspending speed to maintain the pseudo suspension characteristics for the heterogeneous mixture. The effect of solid loading and the binder volume fraction on solid transfer has been reported at room temperature. Two coating regimes are observed (i) heterogeneous coating where particle clusters are formed at a low capillary number and (ii) effective viscous regime, where full coverage can be observed on the substrate. ‘Zero’ particle entrainment was not observed even at a low capillary number of the mixture, which can be attributed to the presence of the binder and hydrodynamic flow of the particles due to the stirring of the mixture. The critical film thickness for particle entrainment is $${h}^{*}=0.16a$$
h
∗
=
0.16
a
for 6.5% binder and $${h}^{*}=0.26a$$
h
∗
=
0.26
a
for 10.5% binder, which are smaller than previously reported in literature. Furthermore, the transferred particle matrices closely follow the analytical expression (modified LLD) of density matching suspension which demonstrate that the density mismatch effect can be neutralized with the stirring energy. The findings of this research will help to understand this high-volume solid transfer technique and develop novel manufacturing processes.
“…The dipping mixture is prepared in 20 mL 95020-0CV Vials, screw top; clear borosilicate glass, round bottom with the dimension of 75.5 × 22.5 mm. The mixture preparation is shown in Figure 1, which is discussed in detail elsewhere 45 .…”
Section: Methodsmentioning
confidence: 99%
“…An in-house dipping station is prepared in our lab for this work. The construction of the dipping setup and the working process are discussed in our earlier work 45 . The dipping experiment is performed at 25 0 C and atmospheric pressure with a low relative humidity of 20%, which allows enough evaporation of solvent from the meniscus during the dipping process.…”
Section: Methodsmentioning
confidence: 99%
“…For submicron size particles, the electrostatic force and van der Waals become prominent for adhering on the substrate due to their possession of a large specific surface area. However, for larger particles (> 1µm), the specific surface area is reduced and which makes them non-interacting and non-agglomerating spherical solid particles in the liquid matrix (non-Brownian regime) 17,44,45 . A density-matching mixture between PEGPG with zinc chloride and neutrally buoyant spherical polystyrene particles with a mean diameter of 80, 145, and 550 µm is reported before by Palma et al 46 .…”
Controlled delivery of inorganic microparticles by the dipping process can open up 3D near-net-shape production techniques through sintering, robocasting or additive manufacturing, and material joining. However, micro-scale inorganic particles (d>1 µm) have reduced surface area and higher density, making them negatively buoyant in dip-coating mixtures and challenging for high yield solid transfer through entrainment due to the density mismatch. In this work, the physical phenomenon of the particle transfer process under stirring energy with negatively buoyant, non-Brownian micro-particles from density mismatching mixture is investigated. Liquid carrier system (LCS) solution is prepared by the combination of a binder polymer and an evaporating solvent. Inorganic micro-particles are dispersed with the assistance of a magnetic stirrer to maintain the suspension characteristics of the mixture. The effect of solid loading and the binder volume fraction on solid transfer has been reported. Two coating regime is observed (i) heterogeneous coating where particles clusters are formed at a low capillary number and (ii) effective viscous regime, where full coverage can be observed on the cylindrical substrate. In our experiment, we have not observed ‘zero’ particle entrainment even at the low capillary number of the mixture, which can be attributed to the presence of binder and hydrodynamic flow of the particles due to the stirring of the mixture. The critical film thickness for particle entrainment is found as ℎ * = 0.16a for 6.5% binder and ℎ * = 0.26a for 10.5% binder, which are smaller than previously reported. Furthermore, the transferred particle matrices are compared with the analytical expression of density matching suspension. The finding of this research will help to understand the high-volume solid transfer technique and develop a novel manufacturing process.
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