Thinning-by-Spinning Mechanism

• Thinning-by-Spinning Mechanism is a family of processes where spinning or twist actively reduces a transverse scale or resistance, such as film thickness, fiber radius, or viscosity.
• The mechanism spans diverse systems including hydrodynamic thinning in spin casting, extensional draw-down in rotary jet-spinning, instability-driven electrospinning, twist-assisted microparticle deswelling, and rheological softening in dense chiral fluids.
• Experimental analyses and scaling laws validate multiple routes—centrifugal, oscillatory, or anisotropic—that couple rotation with thinning, offering insights for optimizing fabrication and material performance.

Thinning-by-spinning denotes a family of mechanisms in which a rotational, spinning, or twist-related process reduces a characteristic transverse scale or a flow resistance. In published usage, the phrase is explicit in the rheology of dense chiral fluids, where microscopic self-spinning lowers macroscopic viscosity (Carenza et al., 12 Jun 2026). Closely related literatures use the same conceptual coupling for hydrodynamic film drainage during spin casting (Karpitschka et al., 2012), centrifugally stretched jets in rotary jet-spinning (Mellado et al., 2011), oscillation-enhanced helical elongation in electrospinning (Coluzza et al., 2014), anisotropic deswelling of bipolar liquid-crystal polymer microparticles into twisted spindles (Ansell et al., 2019), and twist-controlled frictional locking in yarn (Seguin et al., 2021). This suggests that the term does not denote a single universal constitutive law; rather, it identifies several mechanistic routes by which spinning, twist, or helicity is coupled to thinning, slendering, or fluidization.

1. Terminology and conceptual scope

The meaning of “spinning” is context dependent. In spin casting, spinning is literal substrate rotation that drives radially outward flow and film thinning (Karpitschka et al., 2012). In rotary jet-spinning, spinning first ejects the jet and then sustains a centrifugally driven extensional flow that selects the fiber radius (Mellado et al., 2011). In electrospinning under driven perturbations, the relevant “spinning” is the imposed oscillation of the spinneret, which seeds bending instability and lengthens the jet trajectory (Coluzza et al., 2014). In bipolar liquid-crystal polymer microparticles, the closest mechanism is not a hydrodynamic spinning process but a twist-assisted accommodation of anisotropic shrinkage (Ansell et al., 2019). In dense chiral fluids, spinning is microscopic self-rotation encoded through transverse pair forces, and the thinned quantity is viscosity rather than a geometric thickness (Carenza et al., 12 Jun 2026).

The “thinning” is likewise not unique. It can mean reduction of film thickness $h$, reduction of fiber radius $r$, reduction of minor axis relative to major axis in spindle formation, or decrease of shear viscosity $\eta$. In yarn mechanics, the phrase is again only approximate: twist creates a sufficiently slender, sufficiently twisted geometry in which friction is exponentially amplified, and the theory predicts an optimal yarn radius rather than a direct hydrodynamic thinning law (Seguin et al., 2021). A recurring theme across these otherwise disparate systems is that spinning or twist creates either extensional transport, geometric frustration, or an internal stress source that makes a transverse dimension or an effective resistance decrease.

2. Hydrodynamic–evaporative thinning in rotating films

For dilute-solution spin casting, the central thinning-by-spinning mechanism is hydrodynamic–evaporative. Rotation creates a radially outward velocity field in the thin film,

$$u(r,z)=3K\,r\,z\left(h-\frac{z}{2}\right), \qquad K=\frac{\omega^2}{3\nu},$$

so liquid is continuously swept outward (Karpitschka et al., 2012). The corresponding volumetric flux induces a specific vertical advective field,

$\frac{dZ}{dt}=-K z^2(3h-z),$

which matters because the solvent is simultaneously removed at the free surface by evaporation. The film thickness therefore follows

$\frac{dh}{dt}=-2Kh^3-E.$

The cubic term is the hydrodynamic spin-off contribution, while $E$ is the evaporative thinning rate.

This formulation produces a natural crossover thickness and timescale,

$$h_{tr}=\left(\frac{E}{2K}\right)^{1/3}, \qquad t_{sc}^*=(2E^2K)^{-1/3},$$

and the scaled thinning law

$$\frac{d\xi}{d\tau}=-\xi^3-1, \qquad \xi=\frac{h}{h_{tr}}, \qquad \tau=\frac{t}{t_{sc}^*}.$$

The process is therefore divided into a hydrodynamic regime at large $h$, a crossover around $r$0, and an evaporation-dominated regime at small $r$1 (Karpitschka et al., 2012). The same analysis identifies a Sherwood number,

$r$2

which governs whether vertical composition stratification is diffusion dominated or evaporation dominated. In this setting, thinning-by-spinning is not merely centrifugal drainage; it is a coupled radial-outflow, vertical-advection, evaporation, and diffusion problem.

Thermal Marangoni forcing modifies the same classical picture without replacing it. In a rotating cylindrical container of PDMS, a cooler center and warmer edge generate a surface-tension gradient that drives inward surface flow, opposing centrifugal spin-off (Dijksman et al., 2018). The lubrication equation contains centrifugal forcing, Marangoni forcing, gravity, capillarity, and disjoining pressure, and in the central thin-film region the isothermal limit recovers the Emslie-Bonner-Peck law

$r$3

With thermal forcing, the reduced central-thickness equation becomes

$r$4

so early-time thinning remains classical spin-off, but later-time thinning slows and can arrest at

$r$5

This establishes an important boundary condition on the concept: spinning can be the dominant early-time thinning mechanism while other stresses control the late-time morphology (Dijksman et al., 2018).

3. Extensional draw-down in filament formation

In polymer melt spinning, thinning is the direct consequence of extensional draw-down under incompressibility. The one-dimensional slender-filament model uses cross-sectional area $r$6 and axial velocity $r$7, with mass conservation

$r$8

At steady state,

$r$9

and with the nondimensional inlet condition $\eta$0, $\eta$1, and draw ratio $\eta$2, one obtains

$\eta$3

The abstract conclusion is that “the fiber velocity and cross section area are determined solely by the draw ratio” (Sato et al., 2016). The momentum balance,

$\eta$4

then determines how tension, inertia, and viscoelastic stress shape the profile and its stability. In the multiscale dumbbell formulation, each Lagrangian particle contains $\eta$5 Hookean dumbbells, equivalent to the upper-convected Maxwell fluid in the limit $\eta$6 (Sato et al., 2016). Here spinning means axial take-up, and thinning is kinematic draw-down supported by tensile stress.

Rotary jet-spinning realizes a different extensional route. A rotating reservoir ejects a polymeric jet once centrifugal forcing overcomes capillary retention, with threshold

$\eta$7

After ejection, the jet is stretched mainly by a centrifugally driven extensional flow. Combining mass conservation with a balance between viscous elongational stress and centrifugal forcing yields the principal radius law

$\eta$8

The measured radii collapse against the predicted scaling variable, with empirical fit

$\eta$9

and the reported radius range spans roughly $$u(r,z)=3K\,r\,z\left(h-\frac{z}{2}\right), \qquad K=\frac{\omega^2}{3\nu},$$0 nm to $$u(r,z)=3K\,r\,z\left(h-\frac{z}{2}\right), \qquad K=\frac{\omega^2}{3\nu},$$1m (Mellado et al., 2011). Surface tension primarily controls jet initiation and continuity, not radius selection in the successful regime. The minimum angular speed for fiber formation obeys

$$u(r,z)=3K\,r\,z\left(h-\frac{z}{2}\right), \qquad K=\frac{\omega^2}{3\nu},$$2

and the boundary between “beaded fibers” and “no fibers” is fit by

$$u(r,z)=3K\,r\,z\left(h-\frac{z}{2}\right), \qquad K=\frac{\omega^2}{3\nu},$$3

Equally important, solvent evaporation is comparatively slow during flight, with $$u(r,z)=3K\,r\,z\left(h-\frac{z}{2}\right), \qquad K=\frac{\omega^2}{3\nu},$$4, so the jet becomes thin first because of spinning-induced extension and only later dries and solidifies (Mellado et al., 2011).

Electrospinning under driven fast-oscillating perturbations uses yet another route. The spinneret injects the tail bead at

$$u(r,z)=3K\,r\,z\left(h-\frac{z}{2}\right), \qquad K=\frac{\omega^2}{3\nu},$$5

thereby imposing a systematic off-axis perturbation (Coluzza et al., 2014). Coulomb self-repulsion amplifies this perturbation into bending instability and three-dimensional helicoidal structures. Because the jet is incompressible,

$$u(r,z)=3K\,r\,z\left(h-\frac{z}{2}\right), \qquad K=\frac{\omega^2}{3\nu},$$6

so longer helical paths imply smaller cross-sectional area. Increasing oscillation amplitude from roughly $$u(r,z)=3K\,r\,z\left(h-\frac{z}{2}\right), \qquad K=\frac{\omega^2}{3\nu},$$7 to $$u(r,z)=3K\,r\,z\left(h-\frac{z}{2}\right), \qquad K=\frac{\omega^2}{3\nu},$$8 leads to about a three-fold reduction in fiber thickness, with

$$u(r,z)=3K\,r\,z\left(h-\frac{z}{2}\right), \qquad K=\frac{\omega^2}{3\nu},$$9

and

$\frac{dZ}{dt}=-K z^2(3h-z),$0

Increasing frequency from $\frac{dZ}{dt}=-K z^2(3h-z),$1 to $\frac{dZ}{dt}=-K z^2(3h-z),$2 yields roughly a three-fold decrease in thickness as well (Coluzza et al., 2014). Here thinning-by-spinning is best understood as instability-mediated path elongation rather than direct radial squeezing.

4. Geometric twist-assisted slendering in soft solids and fibrous assemblies

In bipolar liquid-crystal polymer microparticles, deswelling from the spherical bipolar configuration causes the microparticle to contract anisotropically and twist in the process, resulting in a twisted spindle shaped structure (Ansell et al., 2019). The system consists of roughly $\frac{dZ}{dt}=-K z^2(3h-z),$3 diameter droplets fabricated from 5CB and RM257 in water with $\frac{dZ}{dt}=-K z^2(3h-z),$4 PVA and $\frac{dZ}{dt}=-K z^2(3h-z),$5 Irgacure 369 relative to RM257. Planar anchoring produces the standard bipolar spherical configuration, and UV polymerization fixes that anisotropic network. Extraction of 5CB with ethanol produces pronounced volume reduction, stronger contraction perpendicular to the boojum-to-boojum axis, and thus transformation into a spindle-like particle with boojums at the tips (Ansell et al., 2019).

The transformation is explicitly two stage. For $\frac{dZ}{dt}=-K z^2(3h-z),$6, shrinking proceeds mainly through inner folding or reduction of effective polymer-strand length with little twist. For $\frac{dZ}{dt}=-K z^2(3h-z),$7, the particle increasingly shrinks by twisting, and the measured $\frac{dZ}{dt}=-K z^2(3h-z),$8 data for $\frac{dZ}{dt}=-K z^2(3h-z),$9 and $\frac{dh}{dt}=-2Kh^3-E.$0 RM257 collapse onto a common curve (Ansell et al., 2019). Representative equilibrium states for $\frac{dh}{dt}=-2Kh^3-E.$1 RM257 range from $\frac{dh}{dt}=-2Kh^3-E.$2, $\frac{dh}{dt}=-2Kh^3-E.$3 in pure chloroform to $\frac{dh}{dt}=-2Kh^3-E.$4, $\frac{dh}{dt}=-2Kh^3-E.$5 at $\frac{dh}{dt}=-2Kh^3-E.$6. The authors model the spiral texture by loxodromes on a spindle surface,

$\frac{dh}{dt}=-2Kh^3-E.$7

with tangent direction

$\frac{dh}{dt}=-2Kh^3-E.$8

For a surface strand of fixed length $\frac{dh}{dt}=-2Kh^3-E.$9, the twist–slenderness coupling is

$E$0

This predicts increased twist angle $E$1 with increasing aspect ratio $E$2. The article’s closest mechanistic description is therefore a geometric twist-assisted thinning mechanism arising from anisotropic shrinkage and fixed-length strand frustration, not angular momentum or forced spinning (Ansell et al., 2019).

An allied geometric mechanism appears in yarn. Twisting makes each fiber follow a helix of radius $E$3 and reduced pitch $E$4. For $E$5, the tension gradient contains an inward radial term,

$E$6

which acts as a twist-controlled harmonic potential (Seguin et al., 2021). Randomly oriented contact normals balance this inward force, and Coulomb friction then gives the local tension-transmission law

$E$7

Hence tension is amplified exponentially,

$E$8

or, in terms of total twist angle $E$9,

$$h_{tr}=\left(\frac{E}{2K}\right)^{1/3}, \qquad t_{sc}^*=(2E^2K)^{-1/3},$$0

The governing nondimensional parameter is the Hercules twist number,

$$h_{tr}=\left(\frac{E}{2K}\right)^{1/3}, \qquad t_{sc}^*=(2E^2K)^{-1/3},$$1

with critical threshold $$h_{tr}=\left(\frac{E}{2K}\right)^{1/3}, \qquad t_{sc}^*=(2E^2K)^{-1/3},$$2 for locking. The theory then predicts an optimal yarn radius,

$$h_{tr}=\left(\frac{E}{2K}\right)^{1/3}, \qquad t_{sc}^*=(2E^2K)^{-1/3},$$3

and for cotton gives $$h_{tr}=\left(\frac{E}{2K}\right)^{1/3}, \qquad t_{sc}^*=(2E^2K)^{-1/3},$$4 and pitch $$h_{tr}=\left(\frac{E}{2K}\right)^{1/3}, \qquad t_{sc}^*=(2E^2K)^{-1/3},$$5, close to the measured $$h_{tr}=\left(\frac{E}{2K}\right)^{1/3}, \qquad t_{sc}^*=(2E^2K)^{-1/3},$$6 (Seguin et al., 2021). This is not thinning of a liquid, but it is a twist-controlled route to a slender, self-locking structure.

5. Rheological thinning-by-spinning in dense chiral fluids

The most explicit modern use of the term appears in dense chiral-fluid rheology. In a two-dimensional Lennard-Jones model with transverse interactions, microscopic self-spinning acts as an intrinsic source of fluctuations and shear, fluidizes a solid, weakens hexatic order, and lowers the apparent viscosity under shear (Carenza et al., 12 Jun 2026). The equations of motion are

$$h_{tr}=\left(\frac{E}{2K}\right)^{1/3}, \qquad t_{sc}^*=(2E^2K)^{-1/3},$$7

with transverse pair force

$$h_{tr}=\left(\frac{E}{2K}\right)^{1/3}, \qquad t_{sc}^*=(2E^2K)^{-1/3},$$8

The chirality parameter is

$$h_{tr}=\left(\frac{E}{2K}\right)^{1/3}, \qquad t_{sc}^*=(2E^2K)^{-1/3},$$9

and the viscosity is defined from the symmetrized off-diagonal stress,

$$\frac{d\xi}{d\tau}=-\xi^3-1, \qquad \xi=\frac{h}{h_{tr}}, \qquad \tau=\frac{t}{t_{sc}^*}.$$0

Two regimes are distinguished. In the solid regime, at $$\frac{d\xi}{d\tau}=-\xi^3-1, \qquad \xi=\frac{h}{h_{tr}}, \qquad \tau=\frac{t}{t_{sc}^*}.$$1, $$\frac{d\xi}{d\tau}=-\xi^3-1, \qquad \xi=\frac{h}{h_{tr}}, \qquad \tau=\frac{t}{t_{sc}^*}.$$2, the passive system does not flow at low $$\frac{d\xi}{d\tau}=-\xi^3-1, \qquad \xi=\frac{h}{h_{tr}}, \qquad \tau=\frac{t}{t_{sc}^*}.$$3, while above a threshold in chirality the system develops a finite zero-shear viscosity (Carenza et al., 12 Jun 2026). In the liquid regime, at $$\frac{d\xi}{d\tau}=-\xi^3-1, \qquad \xi=\frac{h}{h_{tr}}, \qquad \tau=\frac{t}{t_{sc}^*}.$$4, $$\frac{d\xi}{d\tau}=-\xi^3-1, \qquad \xi=\frac{h}{h_{tr}}, \qquad \tau=\frac{t}{t_{sc}^*}.$$5, increasing $$\frac{d\xi}{d\tau}=-\xi^3-1, \qquad \xi=\frac{h}{h_{tr}}, \qquad \tau=\frac{t}{t_{sc}^*}.$$6 reduces $$\frac{d\xi}{d\tau}=-\xi^3-1, \qquad \xi=\frac{h}{h_{tr}}, \qquad \tau=\frac{t}{t_{sc}^*}.$$7. The linear-response viscosity is described by a generalized Green–Kubo relation,

$$\frac{d\xi}{d\tau}=-\xi^3-1, \qquad \xi=\frac{h}{h_{tr}}, \qquad \tau=\frac{t}{t_{sc}^*}.$$8

where the effective temperature is obtained from

$$\frac{d\xi}{d\tau}=-\xi^3-1, \qquad \xi=\frac{h}{h_{tr}}, \qquad \tau=\frac{t}{t_{sc}^*}.$$9

A key result is that $h$0 grows monotonically with $h$1, so chirality can be coarse-grained as an effective heating and fluidization channel (Carenza et al., 12 Jun 2026).

Beyond linear response, the flow curves collapse when expressed in terms of the ratio between imposed shear and spinning rates. Specifically, plotting

$h$2

produces a master curve up to large forcing (Carenza et al., 12 Jun 2026). At larger $h$3, this correspondence breaks down and handedness matters. For $h$4, transverse interactions oppose the imposed shear handedness, string-like flow channels form earlier, and stresses are reduced beyond

$h$5

whereas comparable behavior for $h$6 appears only around

$h$7

This makes “thinning-by-spinning” literal at the rheological level: increasing microscopic spinning reduces macroscopic viscosity in a way quantitatively analogous to shear thinning over a broad regime (Carenza et al., 12 Jun 2026).

6. Boundaries, misconceptions, and adjacent usages

A common misconception is that thinning-by-spinning always implies direct mechanical pulling by rotation. The literature does not support that as a universal statement. In bipolar liquid-crystal polymer microparticles, the authors do not claim that rotation itself actively pulls the body thin as in a mechanical spinner; instead, anisotropic contraction creates a geometric mismatch, and above a threshold aspect ratio the particle loses further volume predominantly through twisting rather than further strand shortening (Ansell et al., 2019). In electrospinning under oscillatory forcing, the thinner fiber arises because helical trajectories lengthen the jet path and increase elongation before deposition, not because oscillation directly squeezes the jet radially (Coluzza et al., 2014). In dense chiral fluids, the thinned quantity is viscosity, and the mechanism is fluidization through transverse nonconservative pair forces and accelerated stress relaxation (Carenza et al., 12 Jun 2026).

Another misconception is that spinning alone determines the final state. Thermal Marangoni forcing in rotating PDMS films shows that early-time thinning can remain classical spin-off while late-time dynamics and equilibrium thickness are set by inward thermocapillary transport (Dijksman et al., 2018). Rotary jet-spinning likewise shows that successful fiber formation requires not only rotational stretching but also sufficiently slow capillary breakup, summarized by the experimentally verified boundary $h$8 (Mellado et al., 2011). In yarn, twist amplification depends on friction, pitch, fiber length, and rupture strain through the single parameter $h$9, not on twist angle alone (Seguin et al., 2021).

There is also a terminological boundary. The paper "Spin Swapping Transport and Torques in Ultrathin Magnetic Bilayers" does not use the phrase “Thinning-by-Spinning Mechanism” and instead analyzes a thickness-controlled crossover in spin transport (Saidaoui et al., 2015). Its core result is that spin Hall effect dominates in the diffusive limit $r$00, whereas spin swapping dominates in the Knudsen regime $r$01, with a qualitative change in torque symmetry from mostly damping-like to mostly field-like (Saidaoui et al., 2015). This is a related thickness–spin coupling, but it is not a thinning-by-spinning mechanism in the hydrodynamic, geometric, or rheological senses described above.

Taken together, these works support a precise but plural usage. Thinning-by-spinning can mean hydrodynamic spin-off of a liquid film, centrifugally driven extensional draw-down of a jet, helical path-length amplification in electrospinning, twist-assisted accommodation of anisotropic shrinkage, frictional self-locking in a slender twisted yarn, or chirality-induced viscosity reduction in dense active matter. What unifies them is not a single microscopic force law, but a recurrent coupling between rotation or twist and the reduction of a transverse scale or flow resistance.