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Nanoscale surface modifications to control capillary flow characteristics in PMMA microfluidic devices.

Mukhopadhyay S, Roy SS, D'Sa RA, Mathur A, Holmes RJ, McLaughlin JA - Nanoscale Res Lett (2011)

Bottom Line: Experimental results presented in detail the surface modifications in the form of distinct changes in the static water contact angle across a range from 44.3 to 81.2 when compared to pristine PMMA surfaces.Additionally, capillary flow of water (dyed to aid visualization) through the microfluidic devices was recorded and analyzed to provide comparison data between filling time of a microfluidic chamber and surface modification characteristics, including the effects of surface energy and surface roughness on the microfluidic flow.We have experimentally demonstrated that fluid flow and thus filling time for the microfluidic device was significantly faster for the device with surface modifications that resulted in a lower static contact angle, and also that the incorporation of micro-pillars into a fluidic device increases the filling time when compared to comparative devices.

View Article: PubMed Central - HTML - PubMed

Affiliation: Nanotechnology and Integrated Bio-Engineering Center, School of Engineering, University of Ulster, Jordanstown, Co Antrim, BT37 0QB, Northern Ireland, UK. s.sinha-roy@ulster.ac.uk.

ABSTRACT
Polymethylmethacrylate (PMMA) microfluidic devices have been fabricated using a hot embossing technique to incorporate micro-pillar features on the bottom wall of the device which when combined with either a plasma treatment or the coating of a diamond-like carbon (DLC) film presents a range of surface modification profiles. Experimental results presented in detail the surface modifications in the form of distinct changes in the static water contact angle across a range from 44.3 to 81.2 when compared to pristine PMMA surfaces. Additionally, capillary flow of water (dyed to aid visualization) through the microfluidic devices was recorded and analyzed to provide comparison data between filling time of a microfluidic chamber and surface modification characteristics, including the effects of surface energy and surface roughness on the microfluidic flow. We have experimentally demonstrated that fluid flow and thus filling time for the microfluidic device was significantly faster for the device with surface modifications that resulted in a lower static contact angle, and also that the incorporation of micro-pillars into a fluidic device increases the filling time when compared to comparative devices.

No MeSH data available.


Curve fitted XPS spectra for three surfaces. (a) C 1s (b) O1s.
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Figure 4: Curve fitted XPS spectra for three surfaces. (a) C 1s (b) O1s.

Mentions: The atomic percentage of chemical species and change to the chemical bonding configurations were probed by X-ray photoelectron spectroscopy (XPS). The corresponding C1s and O1s spectra for pristine, DBD modified, and a-C:H-coated PMMA surfaces are given in Figure 4a,b, respectively. For all the samples studied, the C1s envelope is curve fitted into three components [41-43] at binding energies of 285.0 eV (C-C/C-H), 286.7 eV (C-O), and 289.0 eV (O = C-O). The O1s envelope can be fitted with three peaks at 532.2 eV (C = O), 533.7 eV (C-O/C-H), and 535.0 eV (H2O), respectively [41,42]. The DBD treatment of PMMA clearly shows a loss of alkyl components (C-C/C-H) with a prominent increase in the oxidative groups and generates more hydroxyl components (Figure 4). In general, the DBD atmospheric pressure plasma treatment method generates radicals which, in the absence of other reactants, combine with oxygen from the environment to create oxidative functionalities such as peroxides and hydroperoxides on the polymer surface. The reactive oxygen groups slowly decompose to form more stable oxidative groups such as hydroxyls. A detailed explanation of the oxidation of PMMA observed by XPS analysis after DBD modification has been previously reported by us [44]. In the case of DLC-coated samples, they had less oxygen and hydrocarbon groups. The changes in surface topography due to the surface modifications were probed using an atomic force microscope (AFM). The AFM results suggested that the air DBD process increased surface roughness of pristine PMMA. Both the average and the RMS roughness values increased from 0.71 and 0.90 nm to 2.40 and 3.40 nm, respectively, as shown in Figure 5. It is reported that for surfaces with contact angle less than 90°, the increase of surface roughness reduces the static water contact angle [45]. We have observed that the static water contact angle was much less on the air DBD-treated PMMA than that on the pristine PMMA surface. This type of surface engineering is quite useful in tuning the wettability of the polymer surfaces.


Nanoscale surface modifications to control capillary flow characteristics in PMMA microfluidic devices.

Mukhopadhyay S, Roy SS, D'Sa RA, Mathur A, Holmes RJ, McLaughlin JA - Nanoscale Res Lett (2011)

Curve fitted XPS spectra for three surfaces. (a) C 1s (b) O1s.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211507&req=5

Figure 4: Curve fitted XPS spectra for three surfaces. (a) C 1s (b) O1s.
Mentions: The atomic percentage of chemical species and change to the chemical bonding configurations were probed by X-ray photoelectron spectroscopy (XPS). The corresponding C1s and O1s spectra for pristine, DBD modified, and a-C:H-coated PMMA surfaces are given in Figure 4a,b, respectively. For all the samples studied, the C1s envelope is curve fitted into three components [41-43] at binding energies of 285.0 eV (C-C/C-H), 286.7 eV (C-O), and 289.0 eV (O = C-O). The O1s envelope can be fitted with three peaks at 532.2 eV (C = O), 533.7 eV (C-O/C-H), and 535.0 eV (H2O), respectively [41,42]. The DBD treatment of PMMA clearly shows a loss of alkyl components (C-C/C-H) with a prominent increase in the oxidative groups and generates more hydroxyl components (Figure 4). In general, the DBD atmospheric pressure plasma treatment method generates radicals which, in the absence of other reactants, combine with oxygen from the environment to create oxidative functionalities such as peroxides and hydroperoxides on the polymer surface. The reactive oxygen groups slowly decompose to form more stable oxidative groups such as hydroxyls. A detailed explanation of the oxidation of PMMA observed by XPS analysis after DBD modification has been previously reported by us [44]. In the case of DLC-coated samples, they had less oxygen and hydrocarbon groups. The changes in surface topography due to the surface modifications were probed using an atomic force microscope (AFM). The AFM results suggested that the air DBD process increased surface roughness of pristine PMMA. Both the average and the RMS roughness values increased from 0.71 and 0.90 nm to 2.40 and 3.40 nm, respectively, as shown in Figure 5. It is reported that for surfaces with contact angle less than 90°, the increase of surface roughness reduces the static water contact angle [45]. We have observed that the static water contact angle was much less on the air DBD-treated PMMA than that on the pristine PMMA surface. This type of surface engineering is quite useful in tuning the wettability of the polymer surfaces.

Bottom Line: Experimental results presented in detail the surface modifications in the form of distinct changes in the static water contact angle across a range from 44.3 to 81.2 when compared to pristine PMMA surfaces.Additionally, capillary flow of water (dyed to aid visualization) through the microfluidic devices was recorded and analyzed to provide comparison data between filling time of a microfluidic chamber and surface modification characteristics, including the effects of surface energy and surface roughness on the microfluidic flow.We have experimentally demonstrated that fluid flow and thus filling time for the microfluidic device was significantly faster for the device with surface modifications that resulted in a lower static contact angle, and also that the incorporation of micro-pillars into a fluidic device increases the filling time when compared to comparative devices.

View Article: PubMed Central - HTML - PubMed

Affiliation: Nanotechnology and Integrated Bio-Engineering Center, School of Engineering, University of Ulster, Jordanstown, Co Antrim, BT37 0QB, Northern Ireland, UK. s.sinha-roy@ulster.ac.uk.

ABSTRACT
Polymethylmethacrylate (PMMA) microfluidic devices have been fabricated using a hot embossing technique to incorporate micro-pillar features on the bottom wall of the device which when combined with either a plasma treatment or the coating of a diamond-like carbon (DLC) film presents a range of surface modification profiles. Experimental results presented in detail the surface modifications in the form of distinct changes in the static water contact angle across a range from 44.3 to 81.2 when compared to pristine PMMA surfaces. Additionally, capillary flow of water (dyed to aid visualization) through the microfluidic devices was recorded and analyzed to provide comparison data between filling time of a microfluidic chamber and surface modification characteristics, including the effects of surface energy and surface roughness on the microfluidic flow. We have experimentally demonstrated that fluid flow and thus filling time for the microfluidic device was significantly faster for the device with surface modifications that resulted in a lower static contact angle, and also that the incorporation of micro-pillars into a fluidic device increases the filling time when compared to comparative devices.

No MeSH data available.