|Fabrication and characterization of a surface-patterned thin ﬁlm composite membrane||Journal of Membrane Science||10/17/2013|
Thin ﬁlm composite (TFC) membranes are critical components for reverse osmosis (RO) and nanoﬁltration (NF) processes. Similar to other liquid-based ﬁltration membranes, TFC membranes are susceptible to concentration polarization and fouling/scaling. Recently, surface topography modiﬁcation has been shown as a potential approach for fouling mitigation. However, for TFC membranes, tailoring the surface topography remains a challenge. Here, we demonstrate for the ﬁrst time, successful fabrication of a patterned TFC membrane. A two-step fabrication process was carried out by (1) nanoimprinting a polyethersulfone (PES) support, and (2) forming a thin dense ﬁlm atop the PES support via interfacial polymerization (IP) with trimesoyl chloride and 1,3-phenylenediamine solutions. Chemical, topographic, and permeation characterization was performed on the imprinted IP membranes, and their permselec- tivity was compared with that of a ﬂat (non-imprinted) TFC membrane prepared using the same IP procedure.
|Sajjad H. Maruf, Alan R. Greenberg, John Pellegrino, Yifu Ding||purebluetech.com/wp-content/uploads/2019/07/2014_JMS_Maruf_NIL_TFC.pdf|
|Critical flux of surface-patterned ultrafiltration membranes during cross-flow filtration of colloidal particles||Journal of Membrane Science||08/06/2014|
Previous work has suggested that membrane patterning is apromising approach to fouling mitigation. In this systematic study,we describe performance metrics for the cross-flow filtration of colloidal suspensions through ultrafiltration membranes with lithographically patterned surfaces. The effects of particle size, cross-flow velocity, pattern size, and flow configuration on membrane performance are specifically considered. Using an unpatterned membrane as a reference, results show that the presence of surface patterns increases the critical flux associated with filtration of colloidal feed solutions. For the patterned membranes, the critical flux increases with particle size, cross-flow velocity, the angle between the feed flow and the pattern lines, and the pattern height. These experimental findings can be correlated with a back-transport mechanism such as shear-induced diffusion, which ultimately increases the threshold permeation flux associated with the onset of particle deposition.
|Sajjad H. Maruf, Alan R. Greenberg, John Pellegrino, Yifu Ding||purebluetech.com/wp-content/uploads/2019/07/2014_JMS_Maruf_NIL_colloidal.pdf|
|Use of nanoimprinted surface patterns to mitigate colloidal deposition on ultrafiltration membranes||Journal of Membrane Science||11/16/2012|
Flux decline due to membrane fouling prevails in almost all pressure-driven liquid separations. The factors controlling fouling, ranging from surface chemistry to topographic roughness, have been extensively investigated. However, the role of surface patterns, particularly at a submicron scale, on membrane fouling remains unclear. Herein, we demonstrate that submicron patterns can be success- fully imprinted onto a commercial polysulfone ultrafiltration membrane surface using nanoimprint lithography (NIL) without sacrificing its permeability properties. The presence of these patterns led to significantly improved deposition resistance during filtration of colloidal silica particle suspensions, as evidenced by a 19–45% increase in the apparent critical flux, with the magnitude dependent on particle size. Post-filtration visualization reveals an intriguing anisotropy in the particle deposition, whereby the degree of anisotropy depends on the orientation angle between the surface pattern and the flow direction of the feed. These results suggest a chemical-free route to post-formation, membrane surface modification.
|Sajjad H. Maruf, Liang Wang, Alan R. Greenberg, John Pellegrino, Yifu Ding||purebluetech.com/wp-content/uploads/2019/07/2013_JMS_Maruf_NIL_membrane_particles.pdf|
|Inﬂuence of sub-micron surface patterns on the deposition of model proteins during active ﬁltration||Journal of Membrane Science||05/31/2013|
In this study, the effects of sub-micron surface patterns on the fouling of a model protein solution (bovine serum albumin (BSA)), was investigated during active ﬁltration and simple adsorption conditions. Surface patterns were created directly onto a commercial polyethersulfone ultraﬁltration membrane using nanoimprint lithography, which resulted in a moderately reduced molecular mass cut-off (MWCO) but similar permeance as its non-imprinted counterpart as well as signiﬁcantly improved resistance to BSA fouling. Staged ﬁltration experiments, with backwash cleaning, revealed that the permeate ﬂux of the imprinted membrane was considerably higher than that of the non-imprinted membrane, consistent with UV–vis measurements showing less protein deposition on the imprinted membranes. This improvement in anti-fouling characteristics for the imprinted membrane was universally observed for varying feed-solution chemistry including changes in both pH and ionic strength. From controlled protein-adsorption experiments under non-ﬁltration conditions, it appears that the observed decrease in protein adsorption on the imprinted membranes is likely associated with altered hydrodynamics due to the presence of the sub-micron patterns.
|Sajjad H.Maruf, Melissa Rickman, Liang Wang, John Mersch IV, Alan R. Greenberg, John Pellegrino, Yifu Ding||purebluetech.com/wp-content/uploads/2019/07/2013_JMS_Maruf_NIL_UF_BSA.pdf|