The diminutive force microscope is a adult apparatus which helps abut the characteristics of polymers by absolute concrete backdrop and automated behavior at nanoscale, as able-bodied as accouterment images. This commodity discusses the avant-garde appearance and allowances of Asylum Research CypherTM and MFP-3DTM AFMs in this field.
Polymers are advantageous in a host of applications. Their backdrop can be acquainted and may be customized to clothing altered uses. Moreover, they are generally beneath costly, sturdier and added environmentally affable than added materials. In adjustment to aftermath and accompany into use a new polymer, the structure, processing, characteristics and achievement charge all be understood. This is accessible at micro- or diminutive akin if the abstracts acquired is of this resolution.
Figure 1 shows AFM acceptance in allegory the basal attempt basal polymers, while Figure 2 shows its appliance in engineering a authentic band-aid of a polymer. The point is that AFM plays a basic role in assessing polymers at these baby across scales [1-4]. The aerial spatial resolution brings polymer assay into appearance at resolutions beneath micrometers or alike nanometers. However, abundant added abstracts can be acquired appliance AFMs, such as diminutive forces, mechanical, thermal and electrical mapping, and award the furnishings of calefaction or solvents in astute situations.
Figure 1: Assay of PS-PEP diblock copolymer blur – Borer access appearance angel of a polystyrene-block-poly(ethylenealt-propylene) (PS-PEP) blur on a silicon wafer. The darker arena on the larboard ancillary with lower appearance corresponds to the aerial ancillary of a 16 nm footfall in the wafer. In this arena and the darker arced arena on the right, the blur forms a PS wetting layer. In the lighter arena with college phase, the blur contains a distinct band of all-around PEP microdomains. Several vertical rows of accumbent microdomains are apparent on the low ancillary of the step. Diblock copolymers can cocky accumulate into circuitous alternate structures, a acreage that has admiring absorption for their use as templates in nanolithography. Understanding how blur arrangement and footfall acme affect across breadth and acclimatization aids in developing block copolymer templates. Beheld with the MFP-3D AFM; browse amplitude 2 μm, Z (phase) arrangement 10°. Acclimatized from Ref. 5.
Figure 2: Administration of apparatus in EVA-EPP-carbon atramentous blends – Images of borer access cartography (left) and appearance (right) of semiconducting polymer blends. The blends independent two polyolefin copolymers, poly(ethylene vinyl acetate) (EVA) and ethylene-propylene copolymer (EPP), alloyed with carbon atramentous (CB). The images accord to blends with 10 wt % (top) and 30 wt % (bottom) EPP. Carbon atramentous is an economical accompaniment acclimated in abounding activated applications to actualize electrically administering polymers. However, accession of CB can decidedly affect alloy qualities such as viscosity. The use of two copolymers accomplished a antithesis amid achievement (electrical aggregate resistivity) and processing (melt breeze rate). The appearance images acutely differentiate alone alloy components, acceptance the aftereffect of basic administration on appliance to be studied. Beheld with the MFP-3D AFM, browse admeasurement 20 μm. For added advice see Ref. 6.
Polymer structures change at altered scales of length. These abate arrangement structures accommodate a besom configuration, and if distinct molecules are visualized, alternation packing; for apparent polymers, lamellar formations; and with block or affix copolymers, microphase separation. Appearance arresting on beyond scales accommodate pores or fillers, and for blends of polymers, interfacial phases. Furnishings of processing like etching, calefaction or ache are additionally arresting on the apparent acerbity or finish. The abstraction of nanoparticles, nanofibers and nanodevices fabricated of polymer includes statistical assay of both alone apparatus and the accomplished assembly’s appearance and size.
The AFM allows the anatomy to be visualized via nanoscale cartography of the surface, about in borer mode. This access yields images with accomplished spatial resolution, up to diminutive and diminutive structure, as Figure 3 reveals. The baby across in acquaintance amid the tip and the sample is amenable for the aerial resolution. This in about-face is accomplished by appliance ultrasharp angled probes, in accession to the borer access which after-effects in actual affable alongside and vertical armament amid the tip and the sample.
As Figure 4 shows, AFM imaging has afresh become abundant faster with the actualization of newer AFMs, such as the Cypher AFMs from Asylum Research. This is due to the use of baby cantilevers. Not alone do abate cantilevers accept college beating frequencies, they are additionally able to accommodate bigger resolution and ascendancy for actual baby armament in the subpiconewton range, which is acutely acute back investigating polymers which are aerial and calmly abide deformation.
Figure 3: Diminutive and apparent anatomy of rubrene – Borer access cartography images of apparent rubrene beheld with the Cypher S AFM. Rubrene is a polycyclic ambrosial hydrocarbon acclimated as an amoebic semiconductor in amoebic ablaze abounding diodes. The capital blush angel with browse admeasurement 5 μm shows distinct accomplish of the apparent lattice. The inset black-and-white angel reveals molecular-level structure, highlighting the superb spatial resolution of Cypher AFMs, alike in air. Browse admeasurement 20 nm. Sample address of Rutgers University.
Figure 4: PHB/V spherulite condensate – Borer access appearance images of a polyhydroxybutyrate-co-valerate (PHB/V) spherulite crystallizing at allowance temperature over a aeon of three minutes. Browse admeasurement 1.5 μm. The browse amount of 40 Hz, or about 10 abnormal per frame, allows bright decision of the condensate process. Beheld with the Cypher AFM. Sample address of the University of Sheffield.
The axle acclimated in AFMs is one which is congenital with acute force sensitivity, which makes it ideal for the altitude of a ambit of force magnitudes from piconewtons to micronewtons. This contains best polymer interactions too. There are two accepted means to admeasurement force: either distinct molecules are pulled to assay the armament at diminutive level, or polymeric abstracts are biconcave to appraise their adaptable and viscoelastic acknowledgment afterward deformation.
When the distinct atom access is used, one atom is continued amid the tip of the AFM and the sample surface, and the angle of the axle is measured. Once the bounce connected and angle acuteness of the axle is known, a force vs. ambit artifice is generated. These force curves accommodate advice about intramolecular forces, like the animation of the distinct chain, or conformational transitions, as able-bodied as intermolecular forces, including interactions amid polymer and solvent, and apparent adherence and desorption.
These armament appropriately act central or amid the molecules. One case of force spectroscopy altitude is apparent in Figure 5, appliance poly-L-lysine molecules during their desorption from a berserk surface.
The added adjustment uses abstracts of the angle produced in the axle as the AFM tip indents the sample. Conventionally acclimated cantilevers administer a force that is aerial abundant to account anamorphosis in the polymers which accept modulus alignment from kPa to a few GPa. Back a archetypal is acclimated to appraise the angle of the sample by the tip, abstracts is generated on the adaptable and viscoelastic characteristics of the sample at nanoscale.
Polymers charge accept assertive automated attributes to clothing their assorted applications, such as aliment packaging to adjustable cyberbanking devices. Sometimes one or added apparatus with appearance separation, or a filler, could be added to enhance the automated performance. In best cases they are at nanoscale and appropriately their automated backdrop charge be abstinent at this spatial resolution.
Asylum has assorted techniques for nanomechanical studies, from simple methods of quantitation to avant-garde quantitative techniques. In abounding situations the two are acclimated to accompaniment anniversary added in a way that informs the eyewitness about the polymer sample.
The accession of the borer access for appearance imaging created abundant absorption in the backward nineties. This has led to the actualization of appearance imaging as a actual advantageous apparatus for anecdotic polymers, back it can dness the accomplished anatomy of the atom and assay assorted apparatus of the material.
Sometimes estimation of the after-effects becomes difficult because of the access of the access of accumulator and amusement of adaptable action and adhesive action by the material, respectively, (the accident tangent) in accession to added armament that account dissipation. Yet appearance imaging is still a about accessible and boundless adjustment of accepting qualitative abstracts on actual properties.
Another way to access a qualitative map of actual acreage changes is the use of bimodal imaging or Dual ACTM which is agnate to the borer access with appearance imaging at bottom, with the aberration actuality the active of an added axle access forth with the aboriginal mode. Cartography and appearance abstracts from the aboriginal access are taken forth with amplitude and appearance acknowledgment abstracts from the additional mode. Again, the estimation is sometimes complicated, but its use charcoal authentic for accepting adverse breadth this is not accessible by appearance imaging.
The Asylum NanomechProTM Toolkit lists abounding methods, amid which the altered AM-FM Viscoelastic Mapping Access is ideal for polymers. Like bimodal imaging, this address makes use of borer access to accomplish at two axle access frequencies at the aforementioned time. The additional access is tracked for its abundance and activated with the acerbity of the sample.
The aboriginal access is accompanying to the accident departure of the sample through its appearance and amplitude. The net aftereffect is bright quantitative mapping of the adaptable accumulator modulus and the viscoelastic accident modulus, or accident tangent, but with the acceleration accepted with the borer access and with sample preservation. The ample ambit of applications accessible with the AM-FM mode, authoritative it accessible to assay about any polymer, is because of the absorbing across of its altitude ambit from beneath 1 MPa to over 100 GPa. One instance breadth AM-FM access is acclimated to map a polymer accumulated from assorted apparatus is apparent in Figure 6.
Figure 5: Distinct atom armament for poly-L-lysine polymer – (top) Graphic of force spectroscopy concepts. A distinct polymer atom is covalently absorbed to the AFM tip by a linker (here, polyethylene glycol, PEG). (bottom) Force-distance ambit for poly-L-lysine on a berserk self-assembled monolayer (SAM) in water. The force plateau indicates the desorption of a distinct polymer from the surface. Histograms acquired from assorted force curves accommodate the boilerplate desorption force (inset, top) and disengagement across (inset, bottom) Acquired with the MFP-3D AFM. Acclimatized from Ref. 7.
Figure 6: Automated mapping of a affirmed polymer interface – AM-FM Viscoelastic Mapping Access images and histograms of (left) accident departure and (right) additional access abundance overlaid on cartography for a rubber-epoxy-latex sandwich. Beheld with the Cypher S AFM; browse admeasurement 5 μm. Altered sample apparatus are acutely acclaimed by the AM accident departure of viscoelastic damping. They are additionally bound by the FM frequency, which is proportional to adaptable stiffness, admitting actual agnate modulus ethics for acrylic (~40 MPa) and adaptable (~43 MPa).
Figure 7: Modulus mapping of PS-PCL alloy – Adaptable modulus overlaid on cartography for a polystyrene (PS)-polycaprolactone (PCL) blend. Beheld with Fast Force Mapping Access on the MFP-3D Infinity AFM; browse admeasurement 4 μm. The 1024×1024 angel admeasurement would be impractically apathetic to access with accepted force aggregate techniques. It provides superb crabbed resolution, absolute appearance as baby as about 10 nm. As accepted from aggregate abstract values, PS regions (yellow)have college modulus (approximately 3 GPa) than PCL regions (purple, about 350 MPa). The biodegradable attributes of polycaprolactone is admired in development of new bioblend materials.
Force curves are one accustomed adjustment of adaptable modulus measurement. It is acceptable for back point abstracts are in view, but mapping appliance this address is so apathetic as to be non-feasible. Typically, a 256×256 pixel arrangement is acquired in added than 18 hours, at 1 additional per pixel.
This affair is bound by the Fast Force Mapping Access from Asylum, chip into the MFP-3D Infinity AFM, which has force ambit accretion ante of up to 300 Hz, appropriately demography beneath 10 account to access a 256×256 pixel angel of complete angle vs Z sensor force curves. At this acceleration there are still no curves begin missing nor is there any airy abetment of the data. Figure 7 shows how Fast Force Mapping is agitated out on a phase-separated polymer blend.
Another appropriate adjustment pioneered by Asylum is the Acquaintance Resonance Viscoelastic Mapping Mode, acclimated to admeasurement adaptable accumulator modulus as able-bodied as viscoelastic accident modulus on polymers with about aerial stiffness, modulus of 1 GPa or more.
This access takes advantage of the aerial acuteness of the axle resonance to any baby variations in the automated characteristics of the sample afterwards bringing the tip in contact. In accepted with all these above-mentioned techniques, Acquaintance Resonance can be acclimated either for accelerated qualitative mapping, employing the atomic accessible calibration, or for authentic quantitative after-effects afterwards calibrating adjoin a actual whose backdrop are known.
Many polymers appearance actual cogent changes in backdrop as the temperature increases. It is important to accept bottle alteration temperatures and agnate characteristics in adjustment to accretion a added acumen into diminutive motion. This would accredit the appraisal of backdrop which are analytical to their achievement such as courage and appulse resistance, and to accept how they are afflicted by processing or by aerial temperatures in their operating surroundings.
When AFM abstracts are taken at capricious temperatures, they accommodate abstracts on abounding processes like crystallization, melting, bottle transitions and sub-glass transitions. The use of sample heating stages ensures that temperatures can be assorted with austere ascendancy over the ambit to be advised for polymer transitions. Figure 8 illustrates how modulus in polyethylene terephthalate varies with temperature, this actuality a thermoplastic material. Figure 9 reveals the changes in assay of a microparticle with appearance anamnesis as it undergoes heating.
In accession to assessing the changes in anatomy and backdrop in affiliation to the temperature, there are additionally means to anon assay calefaction backdrop at nanoscale. One is scanning thermal microscopy (SThM), which uses a custom axle distinctively advised to accomplish acquaintance with the sample while ecology the changes in temperature acquired by a bounded calefaction source. As it measures the bounded apparent temperature of the sample, angel adverse is produced in absolute affiliation to the bounded appliance to thermal energy. Figure 10 shows an archetype of SThM acclimated to angel a polymer blend.
Another thermal imaging adjustment is bounded thermal assay (LTA), which uses a delving that is acrimonious locally rather than a bounded sample apparent temperature sensor, to calefaction a nanoscale aggregate of the sample. With heating or cooling of the sample, there is amplification or abbreviating in befitting with its bounded accessory of thermal expansion. The axle angle reflects this change, breeding deflection-temperature curves.
These curves are acutely acute back it comes to audition the alpha of a thermal alteration in the sample, and can appropriately differentiate assorted abstracts by audition their melting or bottle alteration temperatures. The use of this address in testing a ternary polymer alloy is apparent in Figure 11.
Figure 8: Temperature assurance of PET viscoelastic backdrop – (left) Force ambit for polyethylene terephthalate (PET). A 3 additional authority articulation of connected force was activated amid the force loading and auction cycles. (center) Edge curves of angle against time during the force ambit authority interval. The curves accept been normalized to alter amid aught and one, highlighting the access in alleviation time with temperature. (right) Temperature assurance of direct modulus E1(pink squares) and continued appellation modulus E2(black diamonds) acquired by applicable the edge ambit to a three-element Maxwell-Voigt archetypal (inset, center). Both E1and E2exhibit a affecting bead in the temperature ambit amid the glass-to-rubber alteration temperature Tg≈ 77 °C and the PET condensate temperature Tc≈ 13 5°C due to the film’s semicrystalline attributes in this range. Acquired with the MFP-3D AFM and PolyHeater sample stage. Acclimatized from Ref. 8.
Figure 9: Annealing of appearance anamnesis polymer – Borer access cartography images of a polystyrene (PS) microparticle during annealing. Browse admeasurement 12 μm, Z (height) arrangement 1.4 μm. The PS atom was bedfast with a high-temperature, high-pressure nanoimprint lithography (NIL) action and again agilely coated with gold. Imaging began with the atom acrimonious to 80°C. The boiler temperature was rapidly added to 102°C and again added stepwise, so that it was 106°C afterwards 78 min. and 110°C at 170 min. During annealing the atom bore decreases and the acme increases, convalescent the original, pre-NIL all-around shape. A apparent wrinkling assay develops that gives advice on accretion dynamics and ache action release. Applications for micro- and nanoscale polymer particles accommodate biologic commitment and cyberbanking packaging; accumulation appearance anamnesis furnishings could advance to abounding more. Beheld with the MFP-3D AFM. Acclimatized from Ref. 9.
Figure 10: SThM on PP-PS-PE ternary alloy – The sample independent 60% polypropylene (PP), 20% polystyrene (PS), and 20% polyethylene (PE) by weight. In this SThM image, the three apparatus are acutely distinguished, with darker colors agnate to college thermal conductivity. As accepted from abstract ethics for their thermal conductivity, the ellipsoidal regions of PS are brightest (yellow, 0.03 W / m•K), the annular regions of PE are darkest (purple, 0.4 W / m•K), and the surrounding PP cast is average (orange, 0.12 W / m•K).Imaged with the MFP-3D AFM; browse admeasurement 15 μm. Sample address of Dalia Yablon and Andy Tsou, Corporate Strategic Research, ExxonMobil Research and Engineering.
Figure 11: LTA of PP-PE-PS ternary alloy – (top) AM-FM Viscoelastic Mapping Access angel of the aforementioned sample acclimated in Figure 10. The brighter colors announce college modulus. Browse admeasurement 6 μm. The atramentous dots announce credibility breadth LTA abstracts were made. (bottom) The LTA abstracts are blush coded with the credibility in the angel and acutely assay the altered alteration temperatures for PS (blue), PE (green) and PP (red). Sample address of Dalia Yablon and Andy Tsou, Corporate Strategic Research, ExxonMobil Research and Engineering.
In an ambiance that is not at allowance temperature, the change in assay and concrete backdrop over time charge be understood. Back a polymer interacts with a aqueous or breath solvent, the backbone and achievement of the polymer over the continued appellation can go down. In added applications, the acceleration in temperature can affect the lifetime or abidingness of the device.
Once the bread-and-er absorption or thermal gradients are controlled, the added avant-garde AFMs such as the Cypher accept fast browse ante to adviser activating behavior directly, such as abasement or decomposition, alternation and besom ordering, accumulation of lamellae, condensate and melting. It is accessible to access movies assuming the automated or topographical backdrop if the anatomy amount is beneath one minute. In Figure 12, one such instance is apparent breadth the changes in assay action back a broiled polymer recrystallizes.
It is generally difficult to accomplish in borer access appliance solvents or added liquids due to the assorted resonance peaks occurring as a aftereffect of automated coupling amid the borer piezo and the fluid. This has been countered appliance altered techniques appliance assorted actuation platforms. That is, actuation by photothermal, electromagnetic or added armament that brings the assorted peaks bottomward to a few, authoritative it easier to use borer access with added abiding results.
Figure 12: Recrystallization of PP – A alloy of polystyrene (PS) and polypropylene (PP) was acrimonious to 140°C to cook the syndiotactic PP and again cooled at a connected amount while imaging at one anatomy per minute. As the sample cools, the connected PP appearance aboriginal nucleates and again forms partly ordered, semicrystalline regions. Some of the regions anatomy on top of the PS all-around domains. Beheld with the Cypher ES AFM; browse admeasurement 4 μm.
Polymers accept altered characteristics and can be bogus at low costs, apprehension them actual ambrosial for a host of applications like adjustable electronics, photovoltaics appliance amoebic sources, amoebic LEDs, MEMS actuators and sensors, and abstracts accumulator devices. At nanoscale, the electrical and automated backdrop of these abstracts charge be able-bodied understood, and this becomes added basic as miniaturization of accessories proceeds. One decidedly important across is award the alternation amid any bounded heterogeneities and the aggregate performance.
There are specialized modes of AFM operation to appraise the electrical and electromechanical behavior of nanoscale of polymers which accept conductive, semiconducting and dielectric properties. Some of these modes are conductive AFM (CAFM), electric force microscopy (EFM), and Kelvin delving force microscopy (KPFM). These crop electrical abstracts on conductivity, apparent potential, photocurrents and assignment function.
When piezoelectric and ferroelectric polymers are actuality tested, piezoresponse force microscopy (PFM) is acclimated to assay electromechanical behavior at nanoscale, such as animosity switching and across growth. Figure 13 shows how PFM is advantageous in bringing out accomplished detail on ferroelectric polymer nanomesas.
Figure 13: Time-dependent across switching of PVDF-TrFE – (a) Cartography and (b) PFM appearance images of as-grown polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) nanomesa. Browse admeasurement 600 nm, Z arrangement 30 nm (height) and 15° (PFM phase; minimum blue, best yellow). (c) PFM appearance angel of the aforementioned nanomesa afterwards all-around switching due to a DC bent of 6 V. (d-f) Time-dependent animosity acclimatization switching from an activated voltage beating of -5 V afterwards (d) 1 s, (e) 4 s, and (f) 8 s. The almost tip position is adumbrated by the atramentous dot in (a). The aerial electromechanical action of PVDF-TrFe makes it adorable in abounding transducer and sensor applications. Beheld with the MFP-3D AFM. Acclimatized from Ref. 10.
This commodity provides a cardinal of examples to appearance how able the use of Asylum AFMs can be in allegory polymers, whether for accurate or engineering purposes. Newer developments accept fabricated AFMs able to access images to anticipate a cardinal of altered concrete backdrop and behavior as able-bodied as morphology. Asylum AFMs absorb abounding arresting functionalities, such as aerial spatial resolution, accelerated scanning, several operating modes, and so on, which will accredit abounding added characterizations of polymers.
This advice has been sourced, advised and acclimatized from abstracts provided by Asylum Research – An Oxford Instruments Company.
For added advice on this source, amuse appointment Asylum Research – An Oxford Instruments Company.
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