Elementos de la gobernanza en la investigación

2.8.1 Inner-capillary wall vinylisation

This procedure was modified from the one developed by Rohr et al. [75]. A

length of fused-silica capillary was rinsed by flushing with acetone followed by water. Controlled fluid pumping was performed using Hamilton Gastight® syringes and Harvard Apparatus model PHD 2000 syringe pumps. The capillary was flushed with a 0.2M NaOH solution until a basic pH was detected at its terminus, after which flushing was continued for 30 min at 15 μL h-1. The capillary was rinsed with water until a neutral pH was detected, then flushed with a 0.2M HCl solution until an acidic pH was detected, after which flushing was continued for 30 min at 15 μL h-1. The capillary was rinsed with water until a neutral pH was detected, followed by a rinse with ethanol. A solution of 20% w/w 3-(trimethoxysilyl)propyl methacrylate in ethanol adjusted to pH 5 with acetic acid was prepared and flushed through the capillary at 15 μL h-1_{, after which it was rinsed with acetone, dried with compressed}

nitrogen, and stored for at least 24 h before use.

2.8.2 PPM polymerisation mixture preparation

Each polymerisation mixture was prepared in the same way. The following description is for the UVGMA4-70 formulation with BAPO. The reagents used for the other formulations investigated can be found in Table 2.5 on pages 138 and 139. All polymerisation mixtures were prepared using 1 wt% initiator with respect to the monomers. The following reagents were weighed into an amber vial in the order listed: phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (10 mg), glycidyl

methacrylate (0.6 g), ethylene glycol dimethacrylate (0.4 g), cyclohexanol (0.932 g), 1-dodecanol (1.398 g). This mixture was ultrasonicated for 5 min to dissolve the

Chapter 2 | Porous polymer monoliths

initiator, and purged with nitrogen for 10 min. After usage the mixture was stored at -18 °C freezer.

2.8.3 Thermally initiated PPM preparation in fused-silica capillary

Vinylised capillary (250 µm ID) was cut into 30 cm lengths and flushed with polymerisation mixture until no air bubbles were observed. The ends of the capillary were sealed with rubber septa and placed in a 70 °C water bath for 16 h. After removal from the water bath, the capillary was trimmed to 25 cm by cutting equally from both ends and flushed with methanol at 120 μL h-1 _{for 2 h.}

2.8.4 Photoinitiated PPM preparation in fused-silica capillary

Vinylised capillary (100 µm ID) was cut into 35 cm lengths, flushed with polymerisation mixture until no air bubbles were observed, and the ends of the capillary were sealed with rubber septa. For both the OAI Inc. Model 30 and Opto Tech Corp. Shark Series™UV-LED sources, the capillary was coiled up to fit within the exposure area, for the Spectrolinker™ XL-1500 the capillary was straight. The capillary was exposed using either the Model 30, UV-LED, or XL-1500, after which it was flushed with methanol at 30 μL h-1 for 8 h. Finally the capillary was trimmed to 30 cm by cutting equally from both ends.

2.8.5 Photoinitiated PPM preparation in glass microchips

The microchannel wall of the microchips was vinylised using the same procedure as used for capillary. The microchip was filled with polymerisation mixture by pipetting the mixture into both Y wells and putting a minor vacuum on the opposite well using a plastic syringe. Once the channel was full, the single well was sealed using a rubber septa and the mixture in the Y section of the microchannel was removed by placing one of the wells under vacuum using a plastic syringe. Pressure was applied to the single sealed well to move the mixture into the Y section,

Chapter 2 | Porous polymer monoliths

and the removal process repeated. The result was a section of the microchannel at both ends of the chip devoid of polymerisation mixture. All three wells were sealed with rubber septa and tape. The microchip was exposed using either the Model 30, UV-LED, or XL-1500, after which it was placed in a chip holder (described in Chapter 5, Section 5.2) and flushed with methanol at 60 μL h-1 _{for 4 h.}

2.8.6 COC plate grafting adhesion testing

COC plates (75.5 × 25.5 × 1 mm) were cut into two equal pieces and cleaned with acetone and tissue. A mixture of TMPTA (0.5 g) and 3 wt% BP (15 mg) was prepared and purged with nitrogen for 10 min. The mixture was pipetted onto one of the slides until it was covered. A second plate was placed on top of the first then the two plates were clamped together with bull clips along opposite edges of the plates. The plates were exposed for 20 min in the XL-1500 UVC on each face.

2.8.7 COC capillary one-step grafting

A grafting mixture was prepared by weighing MMA (0.5 g), EDA (0.5 g), and BP (30 mg) into a vial, followed by sonication to dissolve the BP. A 12 cm length of COC capillary was filled with the grafting mixture and sealed at both ends using rubber septa. The capillary was exposed in the XL-1500 UVC for 8 min, rotated 180° along the capillary length and exposed again for the same time. Finally the capillary was flushed with methanol and dried with compressed nitrogen.

2.8.8 COC capillary two-step grafting

Two solutions were prepared, an initiator solution consisting of BP (30 mg) in methanol (1.0 g), and a monomer mixture consisting of MMA (0.5 g), EDA (0.5 g), and hydroquinone (25 mg). A 40 cm length of COC capillary was cut and filled with the BP solution, then sealed with rubber septa. The capillary was exposed in the XL-1500 UVC for 20 min, rotated 180° along the capillary length and then

Chapter 2 | Porous polymer monoliths

exposed again for the same time. The capillary was then flushed with methanol, dried with compressed nitrogen, filled with the monomer mixture and sealed with rubber septa. The capillary was exposed in the XL-1500 UVC for 10 min, rotated 180°, and exposed again for the same time. Finally the grafted capillary was flushed with methanol and dried with compressed nitrogen.

2.8.9 Photoinitiated PPM preparation in COC capillary

Grafted COC capillary was cut into 12 cm lengths, flushed with

polymerisation mixture until no air bubbles were observed, and sealed with rubber septa. The capillary was exposed using either the Model 30, UV-LED, or XL-1500, after which it was flushed with methanol at 60 μL h-1 for 4 h. Finally the capillary was trimmed to 10 cm by cutting equally from both ends.

2.8.10Pasteur pipette inner-wall vinylisation

The method used was adapted from that described in Section 2.8.1, scaled up for the larger dimensions using flow rates of 0.1 mL min-1. Three long Pasteur pipettes were placed inside each other such that the tips of each entered the inner neck of the pipette below. Tefzel tubing (1.6 mm ID) was placed in the neck of the top pipette and connected to a syringe.

2.8.11Photoinitiated PPM preparation in Pasteur pipette

Polymerisation mixture was drawn into a vinylised pipette up to the tapered neck and held in place by sealing the other end of the pipette. The tip of the pipette was sealed with rubber septa. The pipette was placed under the light source at a slight angle, to keep the polymerisation mixture from draining into the main chamber of the pipette, and then exposed to form the PPM. Once the exposure was complete, the pipette was placed in a stoppered Büchner flask with only the PPM filled tip inside the flask. The empty top section of the pipette was filled with methanol and a

Chapter 2 | Porous polymer monoliths

vacuum applied to the flask to draw the methanol through the PPM. The pipette was filled with methanol repeatedly until the effluent exiting the pipette tip was clear. The pipette was left in the flask under vacuum for 4 h to dry.

2.8.12COC microchip machining

Milling of the COC microchips was performed by Peter Dove of the Central Science Laboratory, University of Tasmania. The microchips were milled using a flycutter in a vertical milling machine in order to reduce the plate thickness to 0.9 mm for the top and bottom plates. Polishing of the COC microchips was performed by Simon Stephens of the School of Earth Sciences, University of Tasmania. The polishing was done in a two stage process. The first stage involved fine grinding to remove the machining marks and smooth the surface for polishing. A sheet of 1200 wet and dry Silicon Carbide paper was laid out flat on a glass plate wet with water. The chip was laid face down on the abrasive paper and with moderate pressure moved straight back and forth across a small area. Clean water was added frequently to wash away the cuttings. Every 30 sec the chip was rotated though 90° so that the scratches from the abrasive were across one another in order to keep the surface relatively flat. This was continued until the curved machine marks were removed. The second stage of polishing was done with 0.3 µm alumina mixed with clean water on a Pan-W cloth disc. Pressure was approximately 0.5 kg for 3 min at 200 rpm or until the microchip surface appeared shiny. Finally, the polished

microchips were cleaned by first rinsing with water, then flushing 1 mL of a mixture of detergent and water through the microchannel and then sonicating the microchip in the detergent solution for 5 min. The microchip was rinsed and flushed with Milli- Q water, followed by methanol, then dried with compressed nitrogen.

Chapter 2 | Porous polymer monoliths

2.8.13COC microchip grafting

Photografting the COC microchips was performed using a method adapted from that described in Section 2.8.8, using longer exposure times and photomasking. A COC microchip was filled with a BP solution by capillary action and the wells sealed with rubber septa and black electrical tape. The microchannel was also masked with black electrical tape, leaving 4.9 cm of the channel exposed. The microchip was exposed in the XL-1500 UVC for 40 min, flipped over and then exposed again for the same time. Next, the microchip was flushed with methanol, dried with compressed nitrogen, then filled with the monomer mixture and sealed with rubber septa. The microchip was exposed in the XL-1500 UVC for 15 min, flipped over and exposed again for the same time. Finally the microchip was flushed with methanol and dried with compressed nitrogen.

2.8.14Photoinitiated PPM preparation in COC microchip

The grafted COC was filled with polymerisation mixture by capillary action and the wells were sealed with rubber septa and black electrical tape. The ends of the microchip were masked with black electrical tape, leaving 4.9 cm of the

microchannel exposed. The microchip was exposed using either the Model 30, UV- LED, or XL-1500, after which it was flushed with methanol at 60 μL h-1 _{for 4 h.}

2.8.15Glass column preparation and inner-wall vinylisation

Approximately 11 cm lengths of 2 mm and 4 mm ID, 6 mm OD borosilicate glass tubing were cut and the ends rounded using a blow torch. Once cooled, the inner-wall of the columns were vinylised by adapting the method described in Section 2.8.1 for the larger dimensions, using flow rates of 0.1 mL min-1_{. To}

increase through-put, four lengths of glass column of the same ID were joined together with 3 cm lengths of 5 mm ID polyethylene tubing.

Chapter 2 | Porous polymer monoliths

2.8.16Photoinitiated PPM preparation in glass column

A vinlyised glass column was sealed at one end using parafilm and PTFE tape, filled with polymerisation mixture, and then the other end sealed. The column was exposed under the desired light source for the required time. After exposure, the end seals were removed and the column was connected to a 60 mL plastic syringe using 5 mm ID polyethylene tubing. The other end of the column was placed in a 100 mL conical flask filled with methanol. The syringe was used to apply a vacuum to one end of the column in order to draw methanol through it.

2.8.17SEM sample preparation

SEM stubs were prepared by cutting 2 mm thick aluminium sheet into 2 × 1 cm pieces which were bent into right-angle brackets, glued onto 12.7 mm diameter SEM stubs using Araldite™, and allowed to dry overnight. Fused-silica capillary monolithic columns were cut into 5-9 mm lengths from different sections, while COC capillary monolithic columns were scored around the outside at 1 cm intervals using a razor blade and snapped at the score. In a similar fashion, Pasteur pipette monolithic columns were scored around the outside at 1 cm intervals using a ceramic capillary cutter and snapped at the score. Samples were adhered to the upright part of a bracketed stub using carbon tape such that the 4-5 samples were vertical with the tips ~1 mm above the tip of the bracket. Borosilicate microchip monolithic columns were scored down the centre using a ceramic capillary cutter and then snapped in two using two sets of pliers. COC microchip monolithic columns were scored 0.5 mm deep across the width of the top plate of the microchip at 1 cm intervals using a box cutter. The COC microchip was placed in liquid nitrogen for 30 min, after which it was quickly removed and snapped at the score marks using pliers. Parts with clean cross-sections of the monolithic column were broken into smaller pieces and mounted onto bracketed SEM stubs with carbon tape such that the

Chapter 2 | Porous polymer monoliths

cross-sections were facing vertical. These mounted stubs were dried under vacuum for 4-6 h before being sputter coated with gold or platinum.

2.8.18Glass column SEM sample preparation

SEM stubs for mounting glass column sections were prepared in a similar manner as described in Section 2.8.17 except, instead of using aluminium brackets, plungers of 3 mL plastic syringe trimmed to 2 cm from the thumb grip were glued on. This provided a cross-shaped structure to which 3 cm long samples of the 6 mm OD glass monolithic columns were mounted with Araldite™. The column samples were prepared by placing the column in a cordless drill and scoring the outside around the rotation axis with a ceramic capillary cutter at 3 cm intervals, after which the columns were wrapped in paper towel and snapped to the scores.

2.8.19SEM imaging

Scanning electron micrographs were acquired using a FEI Quanta 600 MLA ESEM either in high vacuum or low vacuum mode (0.45-0.6 Torr). Initial

micrographs showed severe charging, Figure 2.16 for example, which is denoted by regions of elevated brightness. Charging is caused by the accumulation of charge on the surface of the polymer which reflects the electron beam through electrostatic repulsion and makes the charged region appear brighter, resulting in a loss of contrast in the image. This was overcome by using the SEM in low vacuum mode where the vacuum in reduced and water vapour introduced into the chamber, which helped reduce the charge accumulation. Most of the SEM micrographs shown were acquired in low vacuum mode at 0.6 Torr with 15-20 kV acceleration voltage and a 3.0 spot size.

Chapter 2 | Porous polymer monoliths

2.8.20Preparation of thermally initiated bulk monolith

Screw thread glass vials (15 × 45 mm) were filled with polymerisation

mixture, sealed, and then placed in a 70°C water bath for 16 h. The vials were broken open to remove the bulk monolith, which was transferred into cellulose thimbles and rinsed with hot methanol in a soxhlet overnight. The thimbles were removed from the soxhlet and dried in a vacuum oven at 60 °C for 4 h, after which the bulk monolith was transferred into 20 mL glass vials.

2.8.21Preparation of photoinitiated bulk monolith using container 1

Container 1 was thoroughly cleaned with methanol and tissue, and then allowed to dry. The container was assembled and polymerisation mixture injected into the chamber through the rubber o-ring using a 25 gauge syringe needle and glass syringe. The container was exposed using either the Model 30 or UV-LED. After exposure, the container was disassembled and the bulk monolith was transferred into a cellulose thimble and rinsed and dried as described in Section 2.8.20.

2.8.22Preparation of photoinitiated bulk monolith using container 2

Container 2 was thoroughly cleaned with methanol and tissue, and then allowed to dry. The quartz disc was placed in a 1M sodium hydroxide bath for 1 h, rinsed with water, placed in a 1M hydrochloric acid bath for 1 h, then rinsed with water and dried. The quartz disc was then placed in a vacuum desiccator with an open vial of trichloro(1H,1H,2H,2H-perfluorooctyl)silane, evacuated and left

overnight. The assembled container was filled with excess polymerisation mixture and then a treated quartz disc was placed in the container. The disc was held in place with the sealing ring and the excess polymerisation mixture removed. The container was exposed using either the Model 30 or UV-LED. After exposure, the container

Chapter 2 | Porous polymer monoliths

was disassembled and the bulk monolith was transferred into a cellulose thimble and rinsed and dried as described in Section 2.8.20.

2.8.23MIP analysis of bulk monolith

Porosimetry analysis was performed using a Micromeritics® AutoPore™ IV 9500 mercury intrusion porosimeter. The dry bulk monolith was broken into pieces small enough to fit into the 3 mL penetrometers, then 0.1 g of sample was placed inside and sealed. Automated analysis was performed on the sample with

equalisation by rate, using 1 to 33,000 psi for intrusion and 33,000 psi to atmospheric for extrusion.

2.8.24Capillary weighing experiment

Monolithic capillary column was prepared using the TCMS1 formulation as described in Section 2.8.3. The monolithic column was dried by attaching the

capillary to a compressed 60 mL plastic syringe, and forcing air through the capillary overnight. The dried capillary was placed in a glass Petri dish and weighed on an analytical balance. Next, the capillary was flushed with ethanol for 30 min at 120 μL h-1, quickly sealed at both ends with rubber septa, and then reweighed. Finally, the mass of the rubber septa was recorded. This procedure was repeated another two times to the same capillary.

Chapter 2 | Porous polymer monoliths

2.9

References

1. Svec, F. and D.M.J. Fréchet, Rigid Macroporous Organic Polymer Monoliths Prepared by Free Radical Polymerisation, in Monolithic Materials -

preparation, properties and applications, F. Svec, T.B. Tennikova, and Z.

Deyl, Editors. 2003, Elsevier. 19-50.

2. Buchmeiser, M.R., Polymeric monolithic materials: Syntheses, properties, functionalization and applications.Polymer, 2007. 48(8), 2187-2198.

3. Svec, F., Porous polymer monoliths: Amazingly wide variety of techniques enabling their preparation.Journal of Chromatography A, 2010. 1217(6),

902-924.

4. Yu, C., M.C. Xu, F. Svec, and J.M.J. Fréchet, Preparation of monolithic polymers with controlled porous properties for microfluidic chip applications using photoinitiated free-radical polymerization.Journal of Polymer Science Part a-Polymer Chemistry, 2002. 40(6), 755-769.

5. Viklund, C., F. Svec, J.M.J. Fréchet, and K. Irgum, Monolithic, "Molded", Porous Materials with High Flow Characteristics for Separations, Catalysis, or Solid-Phase Chemistry: Control of Porous Properties during

Polymerization.Chemistry of Materials, 1996. 8(3), 744-50.

6. Danquah, M.K. and G.M. Forde, Preparation of macroporous methacrylate monolithic material with convective flow properties for bioseparation: Investigating the kinetics of pore formation and hydrodynamic performance. Chemical Engineering Journal, 2008. 140(1-3), 593-599.

7. Urban, J., S. Eeltink, P. Jandera, and P.J. Schoenmakers, Characterization of polymer-based monolithic capillary columns by inverse size-exclusion